I don’t remember how Jellyfin installs on Windows nowadays but if it’s just the Jellyfin tray icon executable giving you issues maybe a simple fix is just to remove it from being autostarted? This is assuming the rest of Jellyfin starts up fine without needing that tray icon in the Windows taskbar.

If that doesn’t help it might be that .NET is broken on your system. That’s a lot harder to fix unfortunately… you could try to see if the Windows add/remove programs gives you an option to re-install/fix the current .net installation but that may not help you out much.

You could also check that your Windows system files aren’t themselves broken. Google around for running SFC and DISM, offhand I typically do something like (in an elevated cmd.exe window):

sfc /verifyonly

if the above tells you there are system files to fix run

sfc /scannow

Restart the computer, repeat the above until sfc tells you there’s nothing to fix.

Then run

dism /online /cleanup-image /scanhealth

if the above tells you there are files to fix run

dism /online /cleanup-image /restorehealth

Restart the computer, repeat the above until dism tells you there’s nothing to fix.

If none of the above fixed anything then it may be time to consider reformatting and re-installing Windows fresh.

(at home I’m on Linux myself but still support Windows systems at work every day)