Use both. Deposit / withdraw huge sums at the bank, always. For small payments, use online banking.

Depending on the bank, online security can be a hit or miss. Are your grandparents ok to learn and do stuff like secure passwords, 2FA…etc? If they are, go ahead with online banking. If not, there is nothing wrong with do the transactions at the bank.

On desktop, it’s easy: Zen Browser, Qutebrowser, Mullvad Browser…etc.

It is the mobile one that is difficult. Literally everything non Chrome sucks.

IMO:

• want to show off? i3wm with gaps and rofi for menu launcher. Add it some transparency effects too.

• want the MacOS style? Gnome. Default on a lot of distros.

• want something stable? XFCE. Install and forget.