Keep in mind that the only reason they deny you the ability to log in to your own local service with your own local sign-in method is that they may upsell you on their cloud junk. If there’d be no cloud account involved - your data would not be at risk and/or leaked. They endangered your privacy for marketing purposes.
If you have not moved off of Plex - do it now. This company is fully rotten.
The email they sent out has reply-to address that conveniently does not work…
How to be innocent (not really): Step 1. Insist that users absolutely MUST use your cloud server for every login into a self-hosted tool on their own hardware. Step 2. Have shit security. Step 3. Ow wow, now users’ data is all over your systems! Hackers clap their hands and do a happy dance. Step 4. Send out “we’re sowwy” email.