Since I've seen a lot of vague posts about the Salesforce OA, here's exactly what I hit.
The online assessment was on HackerRank. Two problems, 90 minute window total. You can split the time however you want.
Problem 1: A string manipulation / parsing problem. Felt like a LeetCode medium. I got through it with a clean solution in about 20 minutes.
Problem 2: A graph problem. BFS variant. Also felt medium, maybe a harder medium. The tricky part was the constraint around disconnected components that you had to handle explicitly or you'd pass 9 out of 10 test cases and miss one.
They do have hidden test cases on HackerRank. I passed all visible ones and 8/10 hidden ones. Still moved forward. So it's not a binary pass/fail on every test case, they look at the overall picture.
The OA comes after the recruiter call. You get a link with a 5-day deadline. Plenty of time, no need to rush.
Tips: Practice clean code, not just working code. I heard from someone inside that reviewers look at code quality when the OA score is borderline. Don't use one language for OA and another for phone screen unless you can defend it. Stay consistent. Python is totally fine. I used it. Nobody said anything.
After the OA I moved to the technical phone screen, which had a different flavor: live coding plus systems conversation. That's a separate thing from the OA.
If you've been grinding LeetCode at medium difficulty you'll be fine here. I did not see any DP or hard-tier tree problems. Just solid fundamentals.