For many demographics nicotine by itself poses a clear health risk. Basically that's pregnant women and anyone under 25 whose brains are still developing, according to the CDC. The WHO further states that nicotine use also increases cardiovascular risk, and that's for everyone. This last one was new to me too until a while ago (although fortunately I never take nicotine in any form).

That is what is left if you ignore the big one, which is its addictiveness. By itself that is probably not directly harmful, but the ways of consuming nicotine mostly are. Nicotine pouches carry some health risks, but are obviously not nearly as bad as snus and other crap like that containing tobacco.