That is the suspension warning you get from Linking.apk, it is just there to tell you to install back the legit playstore version. The ban warning has different wording, don't worry.
Hit OK on this suspension warning and let the title screen reload. After this, tap on Data Link and you should be able to sign in normally to Klab ID. Obviously, don't tap on screen centre because it will just trigger the game to load further and have the suspension warning pop up again. If the warning pop up again before you can tap Data Link, then repeat the process again. I was able to sign in successfully.
After you complete the signing-in process, quit the app. Install Mod.apk over Linking.apk, it will behave like a normal app update.
Once Linking.apk is installed, tap and hold on the app icon > Get Info, turn on Storage and Overlay/Draw Over permissions and you are good to go once you open the app.
As the name suggests, Linking.apk is for account linking only. Mod.apk is the one that you actually play on. They patch over one another, but will never patch over a playstore version. If you ever need to switch between mod and playstore versions, you have to do a full re-install.