Hi R121,
thanks for the report.
Yes, this is expected at the moment. Abandoned Ruins - Combined 0.4.0 is already prepared for Factorio 2.1, but it still depends on the separate AbandonedRuins_updated_fork Core.
The 2.1-compatible Core has not been published on the Mod Portal yet, so Factorio currently cannot resolve the dependency automatically. The Core is maintained by Roland77, and its 2.1 release is therefore outside of Combined itself.
For updates on the Core release, please check the Abandoned Ruins - Updated page or contact Roland77 there.
As soon as the 2.1 Core is available on the Mod Portal, Combined should become downloadable normally as well.
Thanks for your patience!
Greetings
MoSII
