Bill shock abroad is avoidable. A short pre-trip checklist that keeps you online without a nasty surprise from your home carrier.
Roaming charges happen when your home SIM quietly uses the local network at your carrier's roaming rate. The fix isn't going offline, it's controlling which line carries your data.
Before you fly, install a travel eSIM for your destination. On arrival: turn Data Roaming OFF on your home SIM, and turn Data Roaming ON for the eSIM line only. Set the eSIM as your mobile-data line. Now all your internet runs through the prepaid plan you already paid for, your home carrier simply can't rack up roaming.
Leave your home SIM enabled for calls and SMS, so bank OTP codes still arrive, just don't let it carry data. Make calls over the eSIM's data with WhatsApp or FaceTime. That combination gives you full connectivity with zero roaming risk.