My mac desktop will not load eBay.com. When I try to sign on the page flashes 2 times and disappears, then an error page shows up. HELP!

It would be helpful to know what the error message says.

Do you have a similar issue with any other websites that you've noticed?

Reboot your Mac and see if the problem is cleared. If rebooting your Mac doesn’t fix things, see if the problem still happens in Safe mode (hold the shift key down at startup). It can take much longer to safe boot (10 min) so be patient.

How to use safe mode on your Mac - Apple Support 

Safe mode forces the OS to clear certain caches and logs and do other miscellaneous housekeeping. It's non-destructive to user data so is safe to do. Very often certain weird software behavior is corrected by simply logging in this way as a troubleshooting method. When you're in safe boot, the machine will not be at its best performance, especially with graphics, but that's expected.

Does the problem persist while in Safe mode?

Exit safe mode by restarting your Mac normally and re-evaluate the issue again.

If the problem is still unresolved, please return here and post a reply and we’ll see what else we can come up with for help.

Does OK in Firefox ESR 78.14..

https://www.ebay.com/?mkevt=18mkcid=7111608169546898&keyword=conducive&crlp=562786&geo_id=102328&device=computers&cmpgn=216223

Didn't need any quotes. At the most, the < and > on Ends, work OK.

Issues with website page security may be part of the symptoms;

specially in regard to Safari 15.0 and Catalina 10.15.7/Big Sur11.4+

[Often what happens with anything and long URLs,

..the default is marginalized, sure it's there. Kinda.]

Is this a survey or a poll !? LOL😝❄

Did you try to use another browser and see what happens?

No issue using Firefox which is what I do on specific web sites. Perhaps with Monterey Safari will get updated (if not before)