People often cite Hyperloop but he explicitly said he wasn't going to build it himself. They often cite FSD but it is far from abandoned and is driving my car today. What other projects are you thinking of which are actually abandoned? The Tesla solar roof is the biggest one I can think of, I think it's fair to count it as abandoned. I guess the project to make building bricks out of Boring tunnel dirt didn't pan out either, seems pretty minor though.
Boring company maybe? It's not abandoned, but they likely gave up the idea of an underground system of roads under a city, and just focus on single project individually like traditional construction company.
https://x.com/elonmusk/status/888053175155949572 "Just received verbal govt approval for The Boring Company to build an underground NY-Phil-Balt-DC Hyperloop. NY-DC in 29 mins." (July 2017, years after saying he wouldn't build it himself.) Technically it's not a commitment to build, but any other leader in the market would be considered to have failed if they made such a statement and then quietly abandoned it.