Vender lock-in isn't just about data formats, it's about the overall makeup of your infrastructure and development processes. If an org builds around the particular way PlanetScale manages DB branches and other minutiae of their service, they can't simply replace that with an in-house DB server overnight.
True enough, but by that standard, every service would constitute lock-in. A cleaning company isn't lock-in just because you don't have in-house janitors.
"Vendor lock-in" means that you're tied at a business-critical level to some proprietary technology _that you can't get anywhere else_.
If you rent Linux servers, Postgres databases, or even k8s setups from Azure, there's no shortage of alternative vendors willing to sell you compatible product should you tire of MS, and ideally you won't need to change much more than a few endpoints. However, if your entire user base lives in Azure AD, it's a very different story.
It's more like a clever trap, first hit is free etc.
Will be interesting to follow this. I'm not db savvy so I don't mind leaving that job to someone else.