I started using the Portable version to make sure it worked OK.
After two weeks, I'm happy with it and ready to move to the standard version, ie installed in Windows through the installer.
How do I move data from the Portable version to the standard version without losing anything, including settings?
You'd do the reverse of this: https://portableapps.com/support/thunderbird_portable#local_profile
Sometimes, the impossible can become possible, if you're awesome!
Thanks for the tip.