but beware the disk i/o required for recording your video stream, and your SD card and SD card interface's capabilities
might not be an issue... or might be.
Personally, I'd prefer to record to my local NVMe drive, let OBS remux from MKV to MP4 when done (takes maybe a minute for a 7+GB file for me), the I delete MKV and move MP4 to my archive... easy to write simple batch file/script to do the delete and move.
If you computer has an SSD, recognize how spare drive space works with flash and write amplification. though it has been a couple of years, I routinely saw folks fill up an SSD and then wonder why the drive failed after a couple of weeks ... PEBKAC