Yoshi's Story is prob best example. 2D platformer by Nintendo with gorgeous graphics. However, it was a lackluster, forgettable game. Still it proves the 64 was more than capable of exceeding 2D experiences from SNES.
Other examples are StarCraft 64, Bust-a-Move 2, Mortal Kombat Trilogy, SimCity 2000, Killer Instinct Gold (character models 2D), Magical Tetris Challenge, Rampage 2, Ogre Battle 64, MK Mythologies: Sub Zero, Clay Fighter 63 1/2 (2D character models), South Park: Chef's Love Shack, Mischief Makers, etc etc
It was more than capable of exceeding SNES quality graphics on every metric. The RDP on the N64 already had to render 2D rasters that were pre-transformed from 3D projections by the signal processor chip.
Remove that 3D transformation step and allocate some RAM for buffer and you had a perfectly capable 2D platform.
So yeah, it does provide access to the framebuffer, and has a reasonably capable CPU - more or less like PCs of the time did, so of course it's a 'perfectly capable 2D platform' but in this era I don't think we were quite at the point where brute-forcing the graphics pipeline in software was 'easy', and the 2D hardware capabilities were basically nil, compared to SNES or hell Neo-Geo which are very powerful.
It wasn't preventing anyone from producing 2D games, obviously good games could be made, it was just definitely not optimized for that, and that just put more pressure towards 3D, that already had a lot of cultural pressure towards it.
The real impediment I believe was Nintendo themselves... Think about it for a moment. What was the process for publishing to N64? That's right, you had to work directly with Nintendo and effectively get thier stamp of approval (good luck getting enough carts otherwise).
Nintendo didn't want 2d games on thier precious 3d focused console. That simple.
I'd need to go look to recall correctly, but honestly it's 7:30am and I'm waaaay not into doing that rn....
I'm pretty sure the hardware would have given developers a real run for their money to create a SNES-level JRPG experience with smooth, good quality sprite-based graphics. As far as I know it has no 2D acceleration like the SNES, and a very small texture buffer, which leaves slow software rendering directly to the framebuffer, or low quality texture-based sprites. The hardware was really not designed for this type of game, so few were made.
Not providing any hardware to handle those types of games was a function of 3D being all the rage, and the hardware being very clearly targeted at that, but it also meant that creating 2D games was not just out of fashion, but impractical.