Usually this is an antivirus /software firewall issue. But really all I can do is guess.

Why are you not moving your profile from your old laptop? https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer

Thanks for the information! I did so, but it's still not working. The laptop has no antivirus sw and there is no firewall.

Maybe if you share explicit details on how you moved the profile it may offer some suggestions to come forth,

I'm not sure what details you need. I followed directions exactly using a Samsung portable SSD T7 drive.

There is one way to copy and save the passwords and other ways that do not. I was trying to visualize the possibilities. Also, you didn't tell us who your email provider is, as some require unique passwords for each PC. Right now, we know nothing of your situation except that it doesn't work.

It's Zoho, and I tried copying/pasting the password (which is the same on every device) multiple times just in case a character had slipped in.

I can read my mail in the browser on that laptop, logging in to Zoho directly. I was hoping to be able to use Thunderbird instead but if it isn't to be, I can live with that. Thanks for your help.