Once you put a “clean” SIM in a “dirty” smartphone, the SIM becomes dirty, It’s linked to your phones IMEI, and can also be used by companies to track you using your smartphone (eg google play services).
This also works the other way around, though to a lesser extent. Putting a “dirty” SIM in a “clean” smartphone forever links the smartphone IMEI to your phone number, and therefore to your identity.
In other words, if you use your current Bosnia SIM in a grapheneOS device then the government and telco companies can track your location and know your identity. You need an unused* google pixel phone with an unused SIM card.
*unused by YOU. It’s usually fine if you buy a used phone from a stranger.