I've been seeing that nix develop takes a very long time on large projects, and I believe it's due to the whole folder being copied to the store.
nix-shell doesn't have this problem, but I need flakes specifically because they allow to have runtime libraries, which shell doesn't seem to support. (Translating flake.nix to a shell.nix exactly has different execution results.)
What can I do? I've tried putting the flake.nix on an empty subfolder, and it solves it, but it's extremely tedious and clunky.