Edit: I wrote the reply before noticing that I was not in a US-centric sub. That's on me. But the general premise of "No, you can't autodebit" or "Sure, I'll let you think you can auto-debit. Doesn't mean I'll have it turned on at that moment" still holds.

Fidelity does not have an upper limit on the number of cash management accounts one can have. At least not one that I've discovered, as yet.

I've been doing this for years, but for me it's more about sequestering money away from the card that I actively use. Ever sat there for a couple days and realized just how many times Apple will try to hit your card(s) the same day? Same with Amazon.

If that card approves, it's because I'm explicitly trying to pay you, not because some company decided they want to be more aggressive with the autopay.

I don't use Zelle etc for that, when I can help it - look at who runs that service. Yeah, no, not giving you even more data so you can make assumptions about my behavior and intentions.

In addition, I've found multi-currency cards with the ability to set aside money to be useful in the same way. I absolutely do not have trust or a prior relationship with everyone I'm paying over the course of a month, which means I want more control over that process than I normally get.

Is it a pain in the ass sometimes? Sure. But it's also annoying to have to unlock cards when I want to use them - doesn't mean that I forego that extra security. The alternative is bad.