My biggest issue with installing NetBSD, or any other BSD, has been with my own understanding (or misunderstanding) of partition tables, and MBR vs GPT. The second biggest issue is the BIOS & the age of the computer.
UEFI uses the GPT partition table and is the so called "modern way", mainly because it will address disk drives larger than 2TB. My entry into anything beyond Microsoft Windows was learning how to dual boot with Linux. Linux is very sly and uses GRUB to piggy-back on Windows EFI partition. In my dual-booting I migrated to using Rod Smith's rEFInd boot manager, which installs, like GRUB, in among other places, the MS Windows EFI partition. When I got bored with Linux, I moved on to BSD.
BSD has deeper roots, and can use MBR or GPT, but each disk must only have one partition table. You can't have a GPT partition on a MBR drive, you have to decide on the partition table before you can apply individual partitions.
With my older 2014 HP Pavilion, dual-booting meant using a single disk, so I stuck with UEFI & GPT. However, I built me a nice Ryzen7 3700X machine from parts I ordered at Newegg last September 2019. I have a 2TB spinning disk, and a nice little 951GB M2 SSD (twice the size of my old 2014 machine). So now I have a lot more choices.
The first BSD I got to successfully run was FreeBSD. I've been doing that since the middle of last summer, first on older machine, then on the new. FreeBSD works well with GPT, and that keeps me busy running FreeBSD 13.0 Current with a new snapshot installed most every Thursday. But with all the extra space I started working on NetBSD & OpenBSD. I have really been impressed with NetBSD 9.0. I have it running on a MBR install on the entire disk of the older machine. Works great. I have tried putting it on the M2 SSD of the newer machine, and it works there but I'm unable to load X windows with MBR, and I can't seem to get the installer to install it as GPT.
There is something I found out only recently. Not sure why it took me so long:
MBR writes a partition table at the beginning of the drive, but GPT writes a partition table to the beginning AND the end of the drive. So if you just clear the first 512 bytes of a GPT drive and then write a MBR partition table, the old GPT backup table at the end of the drive is still there, unless you deliberately delete it.
All in all I've been enjoying this thread, and continue to learn from it.
Clay