I need confirmation of something not documented anywhere:

myMutableMap.values.removeAll { <predicate> }

Will this remove entries from the map?

Yep. Kotlin mutableMapOf is backed by java.util.LinkedHashMap. LinkedHashMap.values() documentation says:

Returns a Collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa.

... so it really depends on your predicate: for

.removeAll { false }

, the answer to your question is no. 😄

So it depends on the map implementation, that's why it isn't documented in MutableMap