refind-theme-regular VS ursamajor-rEFInd

My boot manager is refind (not grub), and the theme is refind-theme-regular

You can have multiple boot-loader partitions and it will detect them all without any additional setup from user. So if you are dual booting and accidentally formatted boot-loader for one operating system the other will still work. This happened lot of times for me. I accidentally deleted windows option when reinstalling linux a lot. You can also boot from usb directly from refind within needing to go into bios. You also mentioned config file for systemd being simple. Refind also has config file similar to that. And it has theming. I use this theme https://github.com/bobafetthotmail/refind-theme-regular

Theme: https://github.com/bobafetthotmail/refind-theme-regular

I actually managed to get it to work both ways: I can boot each OS in a VM from the other. A handful of scripts inside each detect the VM and make some changes appropriately (like disabling certain startup apps and services that I already have in the host OS, disabling some fancy graphics that like to glitch out in VMs, etc.). And because I like to over-complicate things, I set up static IPv4s, so I can for example connect to Linux with the same IP, not matter if it's in a VM or running on bare metal.

Also, regarding hating GRUB: take a look at rEFInd. The themes are way better [0] and it can autodetect operating systems so not only is it harder to break your system with a bad config, it'll detect USB boot devices as well so you don't have to mash F11 or whatever if you need to boot from one. It also has mouse support and (in theory) also touchscreen.

[0] https://github.com/bobafetthotmail/refind-theme-regular

Finally I installed a simple minimal theme https://github.com/bobafetthotmail/refind-theme-regular and added the OpenCore logo to the icons folder.

I use this one.

For me, Refind it's the best bootloader for dual boot. With a theme like this it's quite pretty : https://github.com/bobafetthotmail/refind-theme-regular

I use this rEFInd theme and convert them into .icns

I would like to switch from grub to rEFInd because it has this specific theme but my main concern is: will it have an option for booting into snapshots? is a handy feature with something breaks on a update but if not that's fine!

If you want to theme refind, I suggest this beautiful theme which has distro icons for all operating systems: https://github.com/bobafetthotmail/refind-theme-regular

Have a look here for some ideas.

I have never tried efistub to be able to provide any insight there, but since you say you like pretty things, GRUB is also themeable, as is rEFInd. I switched to rEFInd a while back solely because (again, though the default is sinfully ugly) it has great themes available. I ended up settling on the Ursa Major theme. I offer this only as a suggestion for possibilities to look into, particularly if you ever want to consider dual booting.