There is nothing more annoying than tons of little repos all of which containing tiny projects with a few hundred lines of code but (of course) you need most / all of them to do anything. Use a mono repo until there is some obvious reason to split it up imo.
On the flip side, we have an org with 50+ teams and our operations team is pinning for a monorepo. They are just fine with one team's push forcing N teams to have an unexpected deploy and recycling of caches, connections, etc. Not to mention what will happen when team A doesn't have time to deal with team B's merge due to other org pressures.
For personal projects, though, I get the value of an actual small projects monorepo.