@Ed No such problem for me.
Slightly special activation (not integrated… you must ask the 6 months license in the program), but successful and mentioned at the bottom of the window.
The program seems to have a menu (three lines at the top right), but it does not open!
Thunderbird is not a “popular” email client apparently.
Scanning the registry only shows part of the installed software (which is often the case with this type of program).
Thank you !