Prohibitory sign crash iMAC 27” late 2014

Mac was very full so I started saving everything from it into an external hard drive. The problems started few days ago when suddenly the background picture was messed up on start up and few things were amiss, like it said keychain doesn't work but then it did and then I started getting prohibitory sign crashes.

Yesterday it got really bad and asked for a chat advice. Guys were useless in a way, two of them were unable to detect that the HDD ejected itself, it did not show up in the list of available drives in Recovery Mode. Second guy made me reinstall the OS wiping everything and instantly solving my full memory problems but Yosemite does not support Photoshop anymore so I upgraded to Catalina. I also had problems signing in to my Apple ID yesterday and access my purchased apps. Only downloaded Logic Pro. Nothing else.

Crashes are worse than before, every five minutes it goes to the prohibitory sign and either it starts up ok to crash again 5 minutes later or it doesn't even start. Machine now empty of everything. I did numerous disc repair options in Recovery Mode , unplugged every external device from it and did the diagnostic for hardware problems it came back with the ADP000 code and the iMac got unresponsive in that mode. I have read Catalina is really bad, but I had not way of using Photoshop in Yosemite which is what I need the most.

Unfortunately because of Covid Genius Bar isn’t open and I cannot take it in for repair. To me it could be a hardware failure, but I know nada about anything. Anybody can suggest any ways to proceed please? Be patient with me please.

Oh and I also have storm bugs under my screen in two places. God knows how they can get in there. I am 90 days out of warranty as well according to Apple’s records. Thank you.