I have a late 2015 build 21.5 inch iMac which I stupidly "upgraded" to Big SLUR 11.2. Now it crashes many times a day. Tex which used to work for my mathematical publishing under Catalina stopped working and it is impossible to get it to work. Nortons doesn't work. Emails go missing. It is slow and many other things don't work. I am resolving this my moving everything over to my Surface book and One drive never to return to the Mac world (I have run both systems since the mid 1980s and have seen how both have ebbed and flowed in terms of reliability etc). Apple is at its nadir now - it is a phone manufacturer and should stop pretending it is in the business of general purpose computers.