Especially if it's affecting his homework and sleep. Tons of parents are dealing with exactly this right now, you're not alone. The thing is, at 14 his brain is still developing and TikTok's algorithms are literally designed to make him addicted - it's not a matter of willpower or discipline, it's very deliberate design. So no, it's not "normal" in the sense of being healthy, even if it happens to a lot of teens.
For the conflict, try approaching it differently than just a flat ban. Instead of telling him "no, it's forbidden," talk to him about the actual problem: homework piling up, sleep messing with his concentration, his mood. A lot of parents say that setting a limit together (like "we decide together that max is 2 hours in the evening") works better than just imposing it. And honestly, technical limits (parental controls, phone out of the bedroom after 9 PM) are less of a punishment than a help - tell him everyone deals with this, that even adults struggle with it.
The other thing that helps: he needs something else to do that actually engages him. TikTok is filling a void. If you can help him find an activity (sport, music, hanging out with friends doing something) where he gets real interactions and little wins, the appeal of the app naturally drops. It takes time but it's more sustainable than just blocking it.