I used to play this a lot but have removed it due to privacy issues
It offers 5 kinds of brain training:
memory, attention, flexibility, speed of processing, and problem solving
I know there are some decent memory training games here on FDroid like Memory
Are there other kinds of brain training games here? (like attention, flexibility, etc)
To be more specific:
One attention game on Lumosity is about directing different colours of trains to their respective station within a few minutes. It trains your attention, speed of processing.
Quite an intense game
Would love to play a FOSS version of this
Or are there similar ones on Linux? (if I may ask here)
Many, many. Search is your friend, but it may take playing a (cough) game with the search to find what you want. Game category + search word in F-Droid app may be a place to start, or web search, patiently.