Launcher unable to authenticate after update

I understand login problems are usually kicked over to Customer Service. However, I think the Linux launcher has a technical problem. The launcher.log has networking errors, launcher-profiles.json looks weird (1970???) and I can log in with the same credentials elsewhere.

I had an issue identical to MCL-22241 and its relatives. The launcher updated itself and broke with the same error in the log. Following their suggestions, I got the launcher to start again by:

1. uninstalling the launcher, 2. deleting .minecraft, 3. reinstalling the following packages via the Synaptic Package Manager:

libc++1 (6.0-2)
libsecret-1-0 (0.18.6-1)
libsecret-common (0.18.6-1)
libstdc++6 (8.4.0-1ubuntu1~18.04)
libstdc++6:i386 (8.4.0-1ubuntu1~18.04)

and 4. reinstalling minecraft-launcher through SPM as well.

The launcher starts now (hooray!) but any attempt to log in results in a message that my email or password is incorrect. It is not. I can log in to minecraft.net and Microsoft just fine. The .deb on the website seems to be an older version than the one I get through the package manager. Installing it just causes the launcher to update itself and break again.

Because of the package shenanigans, I looked up minecraft-launcher's "latest version dependencies" and worked my way through them. Reinstall a few packages, delete .minecraft, reinstall minecraft-launcher, test. If this seems tedious: yes. It didn't work. I've attached a list of all the dependencies I tested.

I appreciate your help. Please let me know if there's any more information I can give you.