While I agree with the majority of the arguments, there are some cases where toolchains make it easier to manage monorepos. With JS/TS we had a monorepo with react web app, react-native mobile app and a shared REST API client library. Once a change was made to the library, tooling bumped library's version based on commit message (conventional commits) then updated the library version in both apps, bumped their versions too and released them to staging. It worked for us and was something that would require more config to achieve with separate repos.

I believe it's up to developers to decide what suits them best based on their requirements, process and tooling.

True however that putting everything in monorepo just for the gist of it is not the best approach.