Not sure if this is a (very annoying) feature or a bug that popped up recently, but when scrolling posts and encountering an ad, it will start playing with sound even though it shows the muted icon, unmuting and muting again has no effect. Sometimes this also happens when there’s no ad in sight, like while reading or replying to a thread, which leaves you with no option than to endure the ad.
This is on v24.03.04-23:28 with Android 13 (T1SSMS33.1-121-4-8). Not sure what other info I can provide to help with the issue.
If you don’t want to buy the ad-free version, consider trying Thunder. It’s the best non-Sync app I’ve used.