I've noticed that if any Thunderbird Portable is running, an installation of another Thunderbird Portable is impossible at the same time.
This is the default behaviour of all Thunderbird Portable installers – in opposite to the Firefox Portable installers!
I run the PortableApps Platform with enabled option 'Check for updates... On platform startup' and enabled option 'Start Automatically' for Thunderbird Portable Legacy 102.15.1.
Then the Platform Updater checks for updates and shows a notification for a new version of standard Thunderbird Portable.
After i click 'Next' to download and continue the installation process, the following message appears:
'Please close all instances of Thunderbird, Portable Edition and then click OK. The portable app can not be upgraded while it is running.'
But the standard Thunderbird Portable isn't running at all.
I think the Thunderbird Portable installers should behave like the Firefox Portable installers. With them, the above scenario is possible.