Readonly reactive variables in pinia store

I am trying to mark a reactive variable in my pinia store as readonly() so it's only changed via setter but doing that yields a warning as

[Vue warn] Set operation on key "value" failed: target is readonly.

[Vue warn] Set operation on key "value" failed: target is readonly.

on initial page load.

How can I solve this?

Readonly reactive variables in pinia store - Nuxt