I've got a pc with multiple drives and I wanted to make it seem like I only had one partition, so I wanted to use an lvm, but It's not a good idea to boot from an lvm, so I thought I could maybe make a small partition for booting and then mount folders like /home and /usr and others on the lvm using fstab (like other guides for moving folders to different drives suggest). I wanted to try it out first, so that I don't end up messing up my computer, so I used an old laptop with kubuntu 20.04. I set up an lvm using two usb sticks and copied the folders to it. Then I edited fstab to mount those folders in the root directory. I stil have copies of the folders in the root directory as well, because those guides say to delete them only after you reboot.
When I try to boot, though, it boots straight into the recovery shell or whatever it's called. If I exclude the entry for /usrin fstab, it does boot, but the screen is just black, except for the mouse pointer. I can move the mouse around, but that's it. No keyboard shortcuts work and not even the power-off button does anything.