Macmail 13.4 on Catalina has stopped connecting to Gmail imap and iCloud imap servers, repeatedly for 5 days now.

This only happens on my Mac mini (late 2012)running Catalina, iPad and iPhone both OK, wifes gmail on MacBook Air running BigSur all ok, gmail via browser all ok.

Have checked mail connection doctor repeatedly, have tried editing server settings, no change, so restored.

Have deleted account and tried to reset account.

Have taken accounts online and offline repeatedly.

iMap.gmail.com and iMap.mail.me.com is trying to connect to port 993 and port 0 alternately neither connects, both using socket 0X0

SMTP servers WERE connecting now they don't appear in the connection doctor.

TLS/SSL tick boxes are unticked.

correct server addresses are checked and rechecked.

Have tried to re-set up account using automatic Google settings.

Internet connection is running at a fairly solid 50-55 Mbps.

Have turned off virus software and Firewall, have turned off VPN.

changed no settings prior to this, and the computer has been running perfectly at this config state for months. I'm at a complete loss as to why this has started NOW. I don't even think there has been any updates to Mac mail behind the scenes that have may have auto installed.

any further ideas? Ideally with known exact examples/screenshots of settings that are currently working, so that I might copy or use them.