Is it possible to BLJ in mario 64 on the switch? sorry if this is a dumb question
No, they ported the shindou version, which doesn't have BLJs.
Long story short, 3D All-Stars is its own game, that's why it has it's own leaderboard that isn't mixed with the original game's. Yes, BLJs are patched, but that doesn't mean the game isn't worth running. 70 Star is one of the most fun categories I've tried in any game, and 120 is still very competitive.
You can actually get the sound affect for the BLJ in 3d all stars by going to either the final bowser, or basement stairs, and then just simply long jump and spam the A button.
The sound of BLJ can easily be heard by BLJing in the LBLJ or SBLJ spot. Other spots like low ceilings also work.
you can BLJ though. hold forward > long jump > hold back > keep long jumping and holding back. simple!