The answer will depend on how many people are working on a single project, what are their skills and knowledge and what tools are in their hands for the Jam.
Both have their PROs and CONs.
2D allows faster implementation of the environment, basic physics and is far easier and faster to produce a good correlation between the gameplay and UI as both uses a similar kind of rendering method.
3D allows faster animations, details' adjustments and allows an easy access to complex physics.
For example, I made a 3D game for the jam : https://itch.io/jam/gamedevtv-jam-2022/rate/1539775
I could have worked on a 2D version of my project, but I would had to put more time in the animations than what I did in 3D. While some part of the game would have been easier to implement in 2D, the perspective of the game would have been affected in a bad way. Ironically, the commercial release I'm currently planning for the project I submitted for this Jam will actually be looking a lot more 2D as I'm not restricted by time anymore.