Your grandparents might be using the wrong reasoning but online banking will open them up to scams. It’s another vector for scammers to get access to their account.

Online banking, itself, is typically very secure. Social engineering is the biggest threat vector.

This is how it goes. The second a politician shows even a fraction less than 100% commitment to the party line, people turn on them. Politics is all black and white and it’s insane. There’s no middle ground.