I've only had one experience with monorepo + microservice, and it wasn't to my taste. As the volume of code sharing increased, the whole thing became ever more monolithic and difficult to change.
Also, if you have a bunch of services all sharing the same schema, you aren't really doing microservices. Not because of some No True Scotsman, "Best practices or GTFO," sentiment, but because that design question, "Do services only communicate over formal interfaces, or do we allow back channels?", is the defining distinction between SOA and microservices. The whole point of the microservices idea was to try and minimize or eliminate those sorts of tight coupling traps.
Also, if you have a bunch of services all sharing the same schema, you aren't really doing microservices. Not because of some No True Scotsman, "Best practices or GTFO," sentiment, but because that design question, "Do services only communicate over formal interfaces, or do we allow back channels?", is the defining distinction between SOA and microservices. The whole point of the microservices idea was to try and minimize or eliminate those sorts of tight coupling traps.