Pi 4; 8GB RAM: Having fimware and OS(openBSD) both on the SD card

Question

Yesterday I installed openBSD on my Pi 4 with 8GB RAM:

1. I first installed the [UEFI firmware][1] on the vfat formated, primary, and only partition of an SD Card
2. I created an openBSD 7.3 boot stick
3. I inserted both in my pi, connected a keyboard and a monitor
4. Everything booted fine and I installed openBSD onto the SD card, which was previously holding the mentioned UEFI firmware
5. I rebooted a few times (while having the USB stick inserted) and everything went fine

I assumed that I had a working setup. However, when I booted the Pi today, I only got a warning that some firmware is missing. I assume, that during the installation process I overwrote the firmware, which was installed on the SD card, with the OS.

An easy solution would be to use the SD card only for the firemware and install the OS on an USB drive. This however, would mean that I waste a huge SD card to only store some firmware and permanently need to connect an USB drive to my PI...

I would prefer to have both, the firmware and my OS, on the SD card. How can this be done?

EDIT: When I insert the USB stick I used for installation it works fine again... Nothing should have been written to this drive, despite the image used for installation. I real don't understand why it boots fine when the drive is inserted and does not if it's missing... [1]: https://github.com/pftf/RPi4

Answer 1

So I just copied the linked firmware (which was still present on the bootable, first partition of the USB drive) to the bootable, first partition on the SD card, which previously only contained the efi/ folder, and this solved the problem.