Thanks @philipp-claßen for such a detailed reply. In my case deployments to production are so tightly controlled by change management with gates etc. that its almost impossible to get changes to prod quickly. While we are moving toward changing our processes, it will take time. Unfortunately, I don't see an alternative other than batching up changes in a release branch.

Thanks @richard-slater. In my case all APIs are internal to the same product dev teams and we have complete control and co-ordinate changes between different APIs and UI, so I am struggling to see what benefits API versioning will provide. IMHO, as per tenets of Trunk based development in order to keep feature branches short-lived, we could also use feature flags to hide features that have not been implemented completely. Correct me if I am wrong...