I noticed in the release notes that 3930R doesn't support OS9.3 or 9.4?
Do you mean the difference between 3390X and 3390R? X vs R seems to mean almost nothing on a Roku model number. Apparently it's just an indication of where you bought it.
Yes, both:
https://developer.roku.com/docs/specs/hardware.md
It should be updated 9.4.0-4200, aside from VPN/geolocation issues (updates sometimes lag outside the US).