[TYPO3-calendar] Migrating from cal 1.7.0 to 1.11 and TYPO3 6 to TYPO3 8.7

[Markus]

Hi,
it's time for our voluntary fire brigade to upgrade from TYPO3 6.2 to 
8.7 with a complete relaunch of the site.

In the moment we are still using cal 1.7 for compatibility issues. We 
are using it to display our google calender on the website.

I have studied the actual cal documentation, but I am still unsure: has 
changed anything from cal 1.7 to 1.11 that I have to keep in mind, e.g. 
when reusing some modified templates e.g. for the list view?

Or is it compatible, so I can simply reuse the modified template files 
and TS statements?

I have seen that TYPO3 isn't using any longer extbase+pibase and all 
extensions now should use extbase+fluid... Hasn't something changed in 
cal as well?

In the extension directory of cal 1.11 I can find the known .tmpl files 
but as well some FLUID template files...

What is the right way to start over with our new website to be 
"future-proof"?

Thanks a lot,

Markus