It might be that your macOS system is too old, unfortunately. Is there any way you can upgrade to a newer macOS system?
Temporarily disabling the 2FA might help also (if still possible at all) as you already tried. I found this instruction how to disable 2FA (but it might be out-dated):
Sign in to Ebay in Safari.
Go to Account > Sign-in and security > 2-step verification > Edit > Use Text
You will be send a code via text, enter it when asked.
Then you will be asked to Verify your email address.
Click Send Code.
You will be send a code via email, so go to your email to get the code and enter it when asked.
You should then see a Deactivate button.
If not, go to: account > Sign-in and security > 2-step verification > Edit
Then the Deactivate button should be visible.