iMac 14,2 not working anymore

Hi All,

I have an old iMac. I downloaded sonoma, also without any problems. I worked with it for two or three months but realized that I needed a newer version for some apps. So I downloaded Sequoia with OCLP.

I have to say that my iMac has two hard disks. One from Samsung, a large one, and an Apple SSD. I tried downloading Sequoia on the Samsung and realized that it wasn't working properly, so I told myself that I would just continue working normally with the old Sonoma on the Apple SSD so as not to break anything else. Now the problem:

But now after using it several times now on restart, something happened that I didn't have before. My background is white it still starts but everything is very slow. Many apps no longer open. Of course I've already read up a lot. Have I really broken everything, do I have to reset everything completely or can I still do/recover something via the OLCP? Can I download everything again?

If I press the ALT key when restarting, it still shows me instsll macOS sequoira. Have I done something completely wrong, do I have to reset it completely, do you think? I would be very happy to hear your opinion!

p.s. sonoma is also still stored as the operating system on the Samsung hard disk. nevertheless with the same error as with the APPLE SSD.

Thank you for your help!