Bethesda confirmed that Doom on the Switch will run at 30 frames-per-second.
According to a statement to Glixel, Bethesda representatives told the publication that "The game and rendering technology underlying Doom is extremely scalable. In bringing Doom to Switch, we targeted outstanding visuals at a solid 30 fps and by maintaining a consistent 30 fps, the experience remains consistently fluid and smooth."
I can confirm that during my preview of Doom on Switch, the action and fps were mostly consistent except for a few occasions, one of which when I used a speedrunning trick that slowed the game down to a crawl. Likewise, I praised the game's visuals for accurately replicating Doom's graphics on the Switch.
Bethesda also revealed that while the main story campaign and Arcade mode will fit on the Switch cartridge (which has a 16 GB capacity), multiplayer will be available as a separate, 9 GB download.
Doom on Switch is currently being developed by Panic Button in collaboration with id Software for the port, with Bethesda publishing the game. You can read our full preview here.