Yesterday I changed the php version to 7.4 and I got these messages in the debug mode so I thought it won't work and I turned it off, but then I turned it on the second time today and I
noticed that the categories have fixed themselves, and in normal mode everything seems to be functioning normally, I'll wait and see if there is any other issues that appear from this, but for now thank you very much.
(one thing I was also curious about, did I somehow trigger the code to update and not be able to work with 5.6 php? or is it more likely it just updated automatically?)