This is a significant bugbear of mine. 
I would very much like to put it back under the … options.
Just to clarify - there was a recent-ish change to start showing the ‘mark as solved’ option outside of the … menu for everyone who has the ability to mark a solution as opposed to only the OP. This is default TL4+, but can be configurable to more people using the accept all solutions trust level plugin setting.