The release notes for Mongoid 5.2.0.rc0 can be found here:
https://github.com/mongodb/mongoid/releases/tag/v5.2.0.rc0
The release notes for 6.1.0.rc0 can be found here:
https://github.com/mongodb/mongoid/releases/tag/v6.1.0.rc0
Both are available from RubyGems:
> gem install mongoid -v 5.2.0.rc0
> gem install mongoid -v 6.1.0.rc0
Please report any issues in our Jira project for Mongoid: https://jira.mongodb.org/browse/MONGOID
Thanks
The MongoDB Ruby team