Is it possible to have systemd-boot remember your last choice and default to that at next boot?
That's the neat part: You don't.
We do not want to write to the EFI variables unless such action is explicitly requested by the user. The EFI variable store is fragile on some machines and it should not be touched by any action during normal operations.
There is the d key for for default, to set the default manually.
Your best bet would be to install GRUB2.
Update, January 2023
I think this is possible now using
Configuring this is a bit hard and unintuitive, so for the uninitiated that's following this thread, here's how to do it in Pop OS:
I suspect the steps are about the same regardless of the distribution.