Hello, I'm wondering which PHP version I could use safely with Projeqtor.
PHP 7.3 / 7.4 / 8.0 ? Right now we are using PHP 7.3

Any will do the job

What about opcache support, is it safe and recommended to enable it ?

Yes it is save and recommended (it accelelrates the server response)
As far as I know, PHP 8.0 does no need opcache any more, as it uses a real comilation phase (not to opcode but to machine code)

It would be nice to have an official Docker image, the community one  HERE is lacking a lot of features (custom image on PHP 5.6 without fpm but opcache seems to be enabled).

Possibly, but this is some work that no one sponsors 🙁 
We are already very busy with new versions, bug fixing, support, ...

I would appreciate to have a reference for the PHP dependencies and stuff (I'm just using the README as a reference).

This is already existing, on the website (search a bit)

Ok I can now confirm that Projeqtor is working fine under PHP8 with opcache enabled (required for JIT as I could see on the web).
I already saw an improvement in loading times.

I would appreciate to have a reference for the PHP dependencies and stuff (I'm just using the README as a reference).

This is already existing, on the website (search a bit)

Yes that's why I said I found the readme.txt which is really complete. I would just appreciate to have not to maintain the configuration at each version upgrade (e.g going back to the readme.txt and find if something changed). Could be done with an official dockerfile, I can give my working Dockerfile if needed.

Thank you for the informations