I tried to move to Typo3 12.4.7 and have problems in converting the typoscript, which works fine under ver 7.6.X
The Screen 
could be obtained, when I change the following lines in the ver 7.6.X script:
# for version 7.X there was: page.1 = TEMPLATE
page.1 = FLUIDTEMPLATE
page.1 {
# the follwing 4 lines are for ver 12.X
templateName = index
templateRootPaths {
1 = fileadmin/templates/webteam
}
The Problem is, the screen with the menus does not fill the contents with the variables.
I have defined the setup.typoscript here in the Typo3 : 
I am novice to Typoscript completly, so where could I debug and search for the reason.
Here is my setup.typoscript script.
page = PAGE
page.typeNum = 0
page.meta.DESCRIPTION = My Site
page.meta.KEYWORDS = Internet, Homepage, Typo3
#page.shortcutIcon = fileadmin/templates/webteam/images/favicon.ico
page.includeCSS {
file1 = fileadmin/templates/webteam/css/cms.css
file2 = fileadmin/templates/webteam/css/base.css
file3 = fileadmin/templates/webteam/css/mug_base.css
file4 = fileadmin/templates/webteam/css/cockpit.css
file5 = fileadmin/templates/webteam/css/menu.css
}
page.bodyTag = <body>
# for versioon 7.X page.1 = TEMPLATE
page.1 = FLUIDTEMPLATE
page.1 {
# the follwing 4 lines are vor ver 12.X
templateName = index
templateRootPaths {
1 = fileadmin/templates/webteam
}
template = FILE
template.file = {$htmltpl}
workOnSubpart = DOKUMENT
subparts.KONTAKT = IMAGE
subparts.KONTAKT.file = {$KONTAKTLINK_BILDDATEI}
subparts.KONTAKT.altText = {$KONTAKTLINK_ALT}
subparts.KONTAKT.wrap = <a href="{$KONTAKTLINK}">| Kontakt</a>
subparts.MENU < temp.Menu
subparts.SUBMENU < temp.Submenu
subparts.FOOTERMENU = COA
subparts.FOOTERMENU{
10 < temp.Footermenu
15 = TEXT
15.value = |
20 < menus.language
}
subparts.INHALT < styles.content.get
subparts.INHALT_LINKS < styles.content.getLeft
#subparts.INHALT_LINKS.select.pidInList = 2
subparts.COPYRIGHT < temp.copyright
subparts.TITEL = TEXT
subparts.TITEL.field = title
subparts.UNTERTITEL = TEXT
subparts.UNTERTITEL.field = subtitle
subparts.SITETITLE = TEXT
subparts.SITETITLE < temp.siteTitel
subparts.BESCHREIBUNG = TEXT
subparts.BESCHREIBUNG < temp.beschreibung
subparts.SUCHE = TEXT
subparts.SUCHE.wrap = <form action="index.php?id={$SUCHID}" method="post" name="tx_indexedsearch">
subparts.BANNER_LINKS = IMAGE
subparts.BANNER_LINKS.file = {$BANNER_BILDDATEI}
subparts.BANNER_LINKS.altText = {$BANNER_ALT}
subparts.BANNER_LINKS.wrap = <a href="{$BANNER_VERWEIS}">|</a>
#subparts.LASTUPDATE < temp.lu
}
## Language ########################################################################################
config {
# only append the language value if not the default language
linkVars = L(1)
# prevent creation of double linkVars www.page.com/index.php?id=12&L=1&L=1
# is just a cosmetical fix
uniqueLinkVars = 1
sys_language_overlay = hideNonTranslated
sys_language_mode = content_fallback
}
# default language (german)
config {
language = de
sys_language_uid = 0
htmlTag_langKey = de
locale_all = de_AT.UTF-8
}
plugin.tx_indexedsearch._DEFAULT_PI_VARS.lang = 0
plugin.tx_pagenotfoundhandler.operator = ODER
# override some language states if english is selected
# Here comes an error
# Thu, 26 Oct 2023 13:16:16 +0000 [ERROR] request="1c1e84830dc3c" component="TYPO3.CMS.Core.TypoScript.IncludeTree.Visitor.IncludeTreeConditionMatcherVisitor": Expression could not be parsed. - {"expression":"globalVar = GP:L = 1"}
#
[globalVar = GP:L = 1]
config {
language = en
sys_language_uid = 1
htmlTag_langKey = en
locale_all = en_US.UTF-8
}
plugin.tx_indexedsearch._DEFAULT_PI_VARS.lang = 1
plugin.tx_pagenotfoundhandler.operator = OR
[global]
## END Language #####################################################################################
My menu.typoscript looks like this:
temp.Menu = HMENU
temp.Menu {
1 = TMENU
1 {
wrap = <table width="100%" border="0" cellspacing="0" cellpadding="0"><tr>|</tr></table>
noBlur = 1
NO = 1
NO {
wrapItemAndSub = <td class="menu1" align="center">|</td>
ATagParams = class=""
ATagTitle.field = description // title
}
ACT = 1
ACT {
wrapItemAndSub = <td class="menu1" align="center">|</td>
ATagParams = class="menuActive1"
ATagTitle.field = description // title
}
}
}
temp.Submenu = HMENU
temp.Submenu {
entryLevel = 1
1 = TMENU
1 {
expAll = 1
noBlur = 1
NO = 1
NO {
wrapItemAndSub = <div class="menu2">|</div>
ATagParams = class="menu2"
ATagTitle.field = description // title
}
ACT = 1
ACT {
wrapItemAndSub = <div class="teasedMenu">|</div>
ATagParams = class="teasedMenuLink"
ATagTitle.field = description // title
}
ACTIFSUB = 1
ACTIFSUB {
wrapItemAndSub = <div class="teasedMenu">|</div>
ATagParams = class="teasedMenuLink"
ATagTitle.field = description // title
}
}
2 < .1
2 = TMENU
2 {
expAll = 1
wrap = <div class="menu3">|</div>
noBlur = 1
NO = 1
NO {
wrapItemAndSub = <div>|</div>
ATagParams = class="level2"
ATagTitle.field = description // title
}
}
}
temp.Footermenu = HMENU
temp.Footermenu {
special = directory
special.value = 192
1 = TMENU
1 {
noBlur = 1
NO = 1
NO {
wrapItemAndSub = |*| | | |*| |
ATagParams = class="menuSpecial1"
ATagTitle.field = description // title
}
}
}
## Language Menu ###################################################################################
# Language switch with TEXT [de] [en]
# set menus.language.1.NO.stdWrap.override = yourGerman || yourEnglish
# set menus.language.1.ACT.stdWrap.override = yourGerman || yourEnglish
# MODIFY IF YOU NEED MORE LANGUAGES
# menus.language.special.value = 0,1
# menus.language.1.NO.stdWrap.typolink.ATagParams = class="german" || class="english"
# menus.language.1.NO.stdWrap.typolink.additionalParams = &L=0 || &L=1
# menus.language.1.ACT.stdWrap.wrap = <span class="active german">|</span> || <span class="active english">|</span>
menus.language = HMENU
menus.language {
wrap = <div id="language">|</div>
special = language
special.value = 0,1
special.normalWhenNoLanguage = 0
1 = TMENU
1 {
noBlur = 1
# Standard Sprachen
NO = 1
NO {
# default title would be the pagetitle need to be override with the language labels
stdWrap.override = <span>[deutsch]</span> || <span>[english]</span>
# remove default link as there would be no GET params
doNotLinkIt = 1
# create new link with current GET params
stdWrap.typolink {
parameter.data = page:uid
additionalParams = &L=0 || &L=1
addQueryString = 1
addQueryString.exclude = L,id,cHash,no_cache
addQueryString.method = GET
no_cache = 0
ATagParams = class="german" || class="english"
}
}
ACT < .NO
ACT = 1
ACT {
stdWrap.typolink >
stdWrap.wrap = <span class="active german">|</span> || <span class="active english">|</span>
}
}
}
TEMPLATEis a completely other object thanFLUIDTEMPLATE.therefore you can't just change the objectname and expect to have the same results.
TEMPLATEhandles marker-templates where replacements is done to markers or subparts marked with markers. typical form:###MYMARKER###FLUIDTEMPLATESare FLUID-templates (hence the name) where replacement is done with variables which are noted like{myVariable}and sections (something like functions or subtemplates)Therefore you need some more work to update a version 7 instance to version 12.
Anyway you will need some intermediate steps as there are not much options to auto-update data structures and configuration from version 7 to version 12. At least your steps should not go farer than 2 versions.
That also belongs to included extensions, which have individual update pathes.