For the last several days i did some further investigation.
first of all. i have to give some background:
as a person that privacy is maybe one of the most important things to me, i was very excited from the idea of nextcloud - a privet cloud. the first time i installed nextloud was 6 months ago.
in order to trust this product and to give my word to lawyers and partners - i wanted to simulate possible problems and try fixing them.
the first simulated problem i created was an assumption that the office router is not working. after that i “replaced” the router to a new one i started the virtuall machine of nextcloud and tried to log to nextcloud. this change of the router caused the problem i discribed above (“internal server error”).
another problem i simulated was that i wanted to check what will happen if the computer is dead - what will happen if i want to move nextcloud to a new pc in the office. so i copied all the files in the attached picture into another pc - and realized that this simulation also causes that problem (“internal server error”).
of course i didnt lose files becuase it is just a simulation and everything is backed-up.
i need at least a year without problems in order to rely on this product. theses days i just install / reinstall and use it only for learning this tool - but i didn’t started yet to use it for buisnees.
i am not a technican - but i guess that maybe after i change a router or copy the files to new pc - maybe i need to write some commands in the terminal in order to fix the problem described…