If I recall correctly, I did that (have had my Gazelle for several months now). popOS! is using LUKS + LVM, Windows Bitlocker. systemd-boot lives on /boot/efi on one nvme SSD, Windows on another. The LUKS/LVM setup also caused a headache, as the installer (at the time) was not able to handle a custom partition layout for the EFI bootloader for the purpose of dual-booting Windows.

I'm not too familiar with the intricacies of the firmware upgrade process (and if it happens, I generally need my laptop and try to fix it as fast as possible ;)), but on every previous firmware update, I had to update the initramfs, run the bootctl installer and in some cases, mess with the systemd-boot loader configs.