That's seriously horrible. There are 5+ open source android apps that I use and want to continue using that are not available on Play Store, but rather through alternative stores (like Zapstore, Obtainium).
If I get a phone with preinstalled Graphene OS (like the upcoming Motorola phone), then does it avoid this stupidity? Or even with Graphene it prevents me from installing apks?
Graphene allows APKs
Having GrapheneOS preinstalled is an option they may discuss with Motorola. It is not the current plan. The current plan is that Motorola release their devices as normal, but some of the flagship devices in 2027 will support manual installation of GrapheneOS.