Can't do screen mirroring from anything my iMac 2012 after upgrading iMac to Sonoma. I can mirror from my iMac 2012 to my MBAs no problem. Airdrop and bluetooth is working fine among all devices. Help!

Hi all! I am losing my mind and am considering buy a new monitor because of this. Been using OCPL to use this old iMac 2012 (quad core i7 intel 16Gb dd3) and it was running smoothly (except when I did a system update via OS instead of OCPL but I digress) then like a month ago or so I can no longer mirror anything to my iMac as it's not displayed on the device list (see pics).

I use this iMac as a second monitor to my work MBA and this is the sole reason I OCPLed it instead of buying something new. I use a USB-C cable to make the display quality better and it was okay until this... I have a personal MBA and a work MBA (both M1, 2021 and 2022) and they can mirror to each other no problem. I can mirror my iMac to both my MBA and also to my tv, but I cannot mirror anything onto my iMac. It worked fine with all Ventura updates and worked fine for a while with Sonoma until then.

I tried a lot of things to fix it: installed the root patches, restarted all computers, log out and in from my iCloud, disabled the firewall in all devices (they are back on now), did the killall sharingd on the terminal, nvram on my iMac, disabled and re-enabled bluetooth (which btw I can see my iMac on both MBAs but it does not connect for some reason). I upgraded my MBAs to Sequoia and then my iMac too but to no avail. File sharing thru Airdrop works from and to all these 03 computers for some weird reason!

As I type this I will downgrade my iMac back to Ventura again but I am running out of options. It's such a shame that I have to buy a new monitor just because I cannot make this work anymore :( it's a 14yo computer but it runs pristinely, it's incredible. Anyways, any help is highly appreciated! Thanks!

this is my personal MBA. In magenta is my work MBA. My iMac doesnt show in the list!