1. Self checkout rarely allow you to pay with cash. 2) Self checkout can be made easier faster by scanning with a phone app

That leads to different complications and outcomes. See OP complaining about slow self checkout. The more self checkout, the less cash transactions and the less privacy.

A fully cashless society would make people more vulnerable. Not just privacy, but maybe some bureaucratic snafu that doesn't allow you a residence, maybe your ID card expired, and no banking account. If you're not in the system, you can't even buy food. Or if your account is in the red and blocked.

Ideally we should have have fully anonymous cash cards. But regulation is being pushed in some countries to limit them, or make you give ID. Or they take 5% "tax" on the revenue. And a phone app is easier to use.