We are treating it as an experiment. Got 2 teams with 5/6 Devs in each sharing the same monorepo. We are using nx.dev as the build tool and it's going pretty well so far.
Different tech stacks too but using nx.dev thats been abstracted away. Allows us to share practices and we've built out the CI/CD and supporting infrastructure on AWS together which has certainly saved duplication of effort. Possibly one more team coming on board too.
If in the future it's not paying off we can always split. Doesn't need to be a forever decision, is how we are viewing it.