Good lock won't work on One UI Core devices. That's what M series phones get, not the regular One UI. You can't. It's using OneUI Core, so it's missing some feature frameworks of the regular OneUI that the GoodLock stuff adds on to.
You don't need to change the CSC for this! Using VPN (sim needs to be removed and clear the data of Galaxy Store app) will allow you to "see" the app in Galaxy Store (and install if compatible). But if your phone is running on One UI Core... you can't install or use Good Lock anyway. Good Lock is built to support One UI devices only.
You must be getting this error probably along with a sentence like "This content isn't compatible with your device". As the other comments mention, One UI Core devices aren't supported by Good Lock, so you can't install it.
