Perhaps I should install the add-ons before restoring a profile, instead of after.

The add-ons *.xpi files are stored in the the folder "extensions" in the Thunderbird profile folder, besides an "extensions.json", an "extension-preferences.json" and an "extension-settings.json" file. So all your add-ons, their settings and their preferences will be saved in a profile backup.

Strange that my add-ons don't show up when I import a backup. Next time, I will add them first, before restoring the backup, and see if their settings are set up. Unless perhaps I am doing something wrong with the backups.

I am probably misunderstanding something here. When I go to the settings of Identity Chooser, the identities do indeed show up, but not in alphabetical order. I have to redo it by hand (over 100 of them). The previous order is not saved, which is something I will ask the developer about.

How do you restore backups? Here are my suggested steps:

here is the info in brief steps:

BACKUP

1. ensure thunderbird is not running
2. enter %appdata% in search window on task bar and press Enter key
3. this should open windows file explorer in Appdata\roaming folder
4. highlight the Thunderbird folder and copy to external media

RESTORE

1. ensure thunderbird is installed and NOT running
2. enter %appdata% in search window on task bar and press Enter key
3. you should be in Appdata\roaming folder , copy&paste the exported Thunderbird folder there. This will prompt to overwrite an existing folder of same name. allow it
4. start thunderbird and all should be there

Strange that my add-ons don't show up when I import a backup.

Maybe your backup was too old and the add-ons were no longer compatible with your new Thunderbird version. Or the add-ons just needed an update .....

No, everything was quite recent, and updated.

Not knowing exactly how you did the backup, I suggest letting this go. Profiles remain intact when copied by windows file explorer and when thunderbird is not running.