FWIW, I received the same email, albeit in German.
I suppose all mails contain a link to the following page which includes somewhat chaotic (IMHO) information.
Here's the link: https://www.memrise.com/blog/changes-to-the-memrise-app?lid=u5wv4x11xsq9
The most important piece of information within the blog post:
All community courses will be retired from memrise.com and the Memrise apps on March 31st. 2024
And:
Community courses will live in the new URL at least until the end of 2024
And last but not least:
Q: Will I be able to access Community Courses on mobile apps?
A: Community Courses will only be accessible on community-courses.memrise.com. They won’t be accessible via the Memrise app past March 31st 2024, but you can use the new website in a mobile web browser and create a shortcut for it on your mobile phone or tablet. You can find instructions on how to do this here for Android, and over here for iOS.
I have tried working on my CCs on my Android mobile in the browser a while ago but found it to be unusable.