Indesign CS5 and Windows 11

Activation may still be a problem, but in theory at least you could as recently as 2019 get an off-line activation through customer support if you persevered. There are some threads about that...

The biggest problem you will have, if you get it installed and running, is there are no partch downloads available. The only technique I know, if you don't have archived patch installers (and I'm not sure there were downloadables) is to copy the program files directory from a patched version after the initial install.

I may have a patched version on an old win7 laptop hanging around if you get that far.

The answer is maybe. You can try to install it and run it in Windows 7 compatibility mode but it's no better than a 50/50 chance. You have nothing to lose by trying.

No, as it is not compatible to this version and you will not be able to acitvate that version.