Close TB, start Profile Manager, create a new profile with a distinct name, then Browse to the folder that was unrecognized. Does the desired profile open in TB?

Did what you suggested. Created a profile called "Test" and the profile wfn4vsvf.test was created. And I see that profile (along with others - default-release, default) The "Test" has nothing in it but a file called times.json. And the profiles that I created in the past, which are also in the profiles folder don't show up. This is what my .ini file looks like:

[Profile2] Name=Test IsRelative=1 Path=Profiles/wfn4vsvf.Test

[Profile1] Name=default IsRelative=1 Path=Profiles/mcdoxkoa.default Default=1

[Profile0] Name=default-release IsRelative=1 Path=Profiles/qb07ihbw.default-release

[General] StartWithLastProfile=1 Version=2

[Install712DAF5A23ABECDC] Default=Profiles/qb07ihbw.default-release Locked=1

This is not how it has looked in the past. It used to be very simple with a path to a profile that I used to just easily change and save. Then I would simply restart TB and the new profile would be there.

When you created the Test profile, did you actually select an older profile folder to define Test, or just create Test as an empty profile? Since the Test profile is at least recognized by TB, you can try copying the contents of one of the other profile folders into Test; delete all files in wfn4vsvf.Test before copying in the files.

I just created a new profile and called it test. It seems to create two profiles when I delete the .ini file, start TB, and let it create a new file. There's a xxxxxxx.default folder with just a times.json file in it and then a xxxxxxx.default-release folder that has all the regular files you would see in a profile. I've never seen that before. Do I need both folders? The .ini file has a "Profile1" with the one filed folder and a "Profile0" with the default. release folder. This never used to be the case. The .ini file used to be a lot simpler (just a path to direct where to find the profile you wanted to use.) And how can I ever access those older profiles that I have saved in the past as backups of my old emails? It looks like things have changed in TB during one of their upgrades? Any advice would be appreciated. Thanks.

The profiles process received a very major overhaul in this last release. I suggest you try and forget just about everything you thought you knew about it and accept that hand editing of the profiles.ini is basically a thing of the past.

This release brought downgrade protection that makes downgrading using an existing profile difficult. This is because there is no attempt going to be made in the future to make profiles backward compatible. So going back will probably loose whatever profile data was converted in this release. Future releases will make huge changes to profiles, like converting the now standard MBOX storage format to the new MailDir format. This alone may see some users loose all their mail if the go back. Going forward again will restore things, but backing out of an update will not be a good idea.

This update also brought profile per install which due the the profile compatibility issues that will creep into the versions basically is designed to upgrade to a new version using an existing profile, but not allow a different version. So you have to actively fight the system using command line options to use the same profile on 2 versions of Thunderbird. No using the same one for beta testing and release for example.

These two things use more than the profiles.ini file. so it is no longer the stand alone arbiter it was. But for a long time we have been recommending folks copy the entire Thunderbird folder in app data from to old to the new device, not just the profile. Those doing so should not encounter these issues