I have to fully agree. They have a discussion on their GitHub [0] about tabs/identation stating that the design goal is to have a non-configurable formatter.

I get the idea behind having a streamlined formatting style, but I’m really not a fan of denying users the flexibility to adjust it to their needs. Consistency across projects is nice, yet forcing everyone into a single indentation style feels unnecessarily rigid. A little configurability would go a long way :)

[0] https://github.com/gleam-lang/gleam/discussions/3633