You should really not need to do a PR across multiple repos.

different ways of treating PRs… it’s a perfectly valid strategy to say “a PR implements a specific feature”, in which case you might work in a backend, a front end, and library… of course, those PRs aren’t intrinsically linked (though they do have dependencies between them… heck i wouldn’t even say it’d be uncommon or wrong for the library to have schemas that do require changes in both the fronted and backend)

if you implement something in eg the backend, and then get retasked with something else, or the feature gets dropped then sure it’s “working” still, but to leave unused code like that would be pretty bad… backend and front end PRs tend to be fairly closely tied to each other

a monorepo does far more than i think you think it does… it’s a relatively low-infrastructure way of adding internal libraries shared across different parts of your codebase, external libraries without duplication (and ensuring versions are consistent, where required), and coordinating changes, and plenty more

can these things be achieved with build systems and deployment tooling? absolutely… but if you’re just a small team, a monorepo could be the right call

of course, once the team grows in size it’s no longer the correct option… real tooling is probably going to be faster and better in every way… but a monorepo allows you to choose when to replace different parts of the process… it emulates an environment with everything very separated