What do I need to do?

I got the email about the Tidal removal. But I’m confused what i need to do? Ho do i continue with just Plex Pass, I don’t want to change my account.

You don’t need to.
Just let the current subscription expire.
Afterwards, you can subscribe again for a regular Plex Pass, if you want to continue using its features.

If I let my Plex subscription expire, I should renew using my Plex account?

How about my Tidal playlists etc? If I want to continue with Tidal, what account do I need to use?

All information relating to this will be communicated by Tidal in a separate email.
It will no longer have anything to do with Plex in any way.

Yes. Plex Pass is always applied to a Plex account.

Has anyone received an email from Tidal on how to keep their Tidal subscription active after the integration with Plex ends?