> I once moved a system that had one unencrypted partition for everything and booted in BIOS mode, to two encrypted partitions for `/` and `/home` that booted in UEFI mode [...]
I've done this a bunch of times. First from a single partition on a spinning disk 7 years ago to slowly migrating more and more parts onto SSD's as they became affordable, then converting the root to GPT, and finally merging it all back when I finally had an SSD big enough to store all of it. You just make your new partitions and rsync it all on there. The most important part is keeping all of the file attributes, but the correct rsync flags take care of that. Then you just need to update your fstab and bootloader and you're basically golden. It's been quite simple.
The key for me has been to keep the old stuff in place for a first boot so that I could easily recover if I fucked it up. I've never needed it, but it was a nice feeling of safety.
I've done this a bunch of times. First from a single partition on a spinning disk 7 years ago to slowly migrating more and more parts onto SSD's as they became affordable, then converting the root to GPT, and finally merging it all back when I finally had an SSD big enough to store all of it. You just make your new partitions and rsync it all on there. The most important part is keeping all of the file attributes, but the correct rsync flags take care of that. Then you just need to update your fstab and bootloader and you're basically golden. It's been quite simple.
The key for me has been to keep the old stuff in place for a first boot so that I could easily recover if I fucked it up. I've never needed it, but it was a nice feeling of safety.