Your saved passwords should be in the old profile... the Master & the email words..
Unless you didn't save them in the Tbird program and typed them in each time?
I’ve done this many times with trying out various Linux distros..and past Windows crashes, when I still used Windows.
How to import your old profile into the new Tbrid program....
Install fresh newest version of Tbird from Mozilla - click to open it, when the screen to add email account or make one comes up, just close the program.
plug in external drive or a flash drive so you can access the old saved profile.
this is easier that me typing it all out-
[ Note: If you just installed Thunderbird on a new computer, you can use the default profile that is automatically created when you first run Thunderbird, instead of creating a new profile.
Locate the backed up profile folder on your hard drive or backup medium (e.g., your USB-stick).
Open the profile folder backup (e.g., the xxxxxxxx.default backup).
Copy the entire contents of the profile folder
backup, such as the mimeTypes.rdf file, prefs.js file, bookmarkbackups folder, etc.
Locate and open the new profile folder as explained above and then close Thunderbird (if open).
Paste the contents of the backed up profile folder into the new profile folder, overwriting existing files of the same name.
Start Thunderbird. ]
full details here- https://support.mozilla.org/en-US/kb/profiles-tb
But if it is the Master Password to open the Tbird program, and you forgot it, I believe you can find the certain file and delete it so no password , then you can make a new password..
[Forgotten Password (Tbird)
If you have lost or forgotten your master password or you want to disable the feature, you can reset the master password. Resetting the master password will remove all stored password information. Upon resetting, you will lose all the stored information in the Password Manager, as this is a built-in security feature to prevent people from simply resetting your Master Password to gain access to your passwords.
Choose Tools -> Error Console
Paste the expression
Press the Evaluate button.
Accept when prompted with the confirmation dialog box. ]
If you do that , you will still have your backup files accessible to replace passwords to the email account/s , if you don't have them memorised..or written down..
If those ideas don't help, them I am totally confused about what password you need..