Thunderbird Profiles
The profile manager goes out of it's way to provide all possible options *except* the one that's needed most:
How to simply "switch" from one profile to another profile?
When a new Thunderbird installation is created, all profile operations are limited to the profiles created when Thunderbird is installed. Other profiles that are available in the right location under Users\---\AppData\Roaming\Thunderbird\Profiles\* are simply ignored without any possible, or at least obvious, route to switch to them and / or activate them. Why?
This issue is a real problem when attempting to migrate existing Thunderbird settings, mail data, etc., from one physical workstation to another. Fortunately I found a fix by grabbing the mail\pop_account folder under the old profile and plugging that folder into the new profile. Still there was additional aggravation associated with lost settings, another import / export for the calender, etc., etc.
Again, why does this have to be difficult?
Alla svar (1)
Actually, it's not difficult, yet you picked the hardest way. Moving a profile is rather straightforward, as this URL indicates:
https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer and switching between profiles is not a recommended way to do that. However, there are times (not this one) where changing profiles is desirable, and the profile manager does a nice job of that: https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-thunderbird-profiles