I expect this is not new and should work. At least it apparently does not work on openSUSE Linux, current Tumbleweed-Slowroll, Gnome 49.4 and Thunderbird v.140.8.0-1.0.4.1.sr20260202 .
This happends: selecting one or more files in Gnome Files, right-click and Email from the context menu: a Thunderbird email message window opens, but no attachments there or any suggested subject filled in. Thunderbird is set as default email and calender app. (In comparison Email link from Firefox to Thunderbird does work)
The corresponding feature works on Android (share) Gmail, and other earlier email clients, Seamonkey and maybe also GroupWise and earlier Thunderbird (?)