@MDLefevere Pi4 or Pi3? With the Pi4 there is at the moment only the “dual” option: you have to have inserted a sd-card, so the boot partition stays on the sd, but everything else is going to the SSD. That works very well until the RPi foundation comes up with a solution to boot directly from SSD. What I’ve read, I wouldn’t expect that to happen soon…
I’m just working on a small write-up about the installation on a Pi4, because the tutorial I used isn’t totally clear and didn’t work as such for me, but here it is anyway: Rpi 4 installation - Installation - Home Assistant Community
With the Pi3 there is an option to set, afterwards the Pi3 is really booting from SSD.