This is an issue for portableapps.com. You can download ver 91 there and upgrade from it.

Thanks for reply, But - what shall this change? Also, my question was about downgrading, not upgrading. I want to get to previous version (it's 102 I think)

Hi

This really is a question that the team at portable apps should be able to help you with.

Try this link for 102 Portable: https://portableapps.com/apps/internet/thunderbird-portable-legacy-102

If you install this to a different folder than the current one, you may be able to copy the profile folder from your current installation (it's in your Thunderbird Portable\Data folder) and paste it in place in the new installation. But before you run the new 102, after you copy and paste (in Data. Create the Data folder if it's not there, then open that empty folder and paste the profile folder into it.) the profile folder, open that folder and delete the file "compatibility.ini". Whatever you do, don't just install the older edition into the same folder as your current version. That way, if everything doesn't work out for you, you still have the current installation to work from to achieve your goal. And you can simply delete the new 102 installation and start again. Maybe call the new installation "Thunderbird Portable Legacy," not just Thunderbird Portable.

Wisewiz Thank you SO MUCH This seem to work just fine Why TB had to screw itself, no idea. But glad that at least for some time I'll be able to use a normal email client, still. Really appreciate.

@HeavyMetal

You're most welcome. Good luck with 102, and remember to uncheck "Automatically install updates." Settings > General > Updates