These days, Standard uses gVisor so there are fewer and fewer constraints. Most things just work.

Flex really is for the edge cases where you need really big instances or really long execution times.

(I used to work at GCP)

Or, annoyingly, websockets.

Yeah, it seems like all the new infrastructure features (websockets, gRPC, GBLB, VPC, etc) are coming to Cloud Run instead of App Engine.

Websockets are fine on flex, but yeah, Cloud Run is getting the love these days.