That's really useful (I was trying to work out how to do this without using a custom image) but I would just note that there actually is a FreeBSD 13.1 image available under Images -> Partner Images -> FreeBSD (from the FreeBSD Foundation).
Oracle Cloud have a very generous free-tier for the arm64 boxes and I'm running 2 x arm64 instances (2 CPU / 12GB RAM each) - been really reliable so far though I'm not doing that much on them.
Thank you for pointing that out! I could've sworn it wasn't there when I checked. It seems it was added recently, but only for arm64 [1]. I will add a note to the post about this.
Oracle Cloud have a very generous free-tier for the arm64 boxes and I'm running 2 x arm64 instances (2 CPU / 12GB RAM each) - been really reliable so far though I'm not doing that much on them.