They’re not legal to import as far as I’m aware, and the Taiwanese government appears to be becoming more rather than less strict on stuff like this.
From what I understand, snus isn’t legal to import because it’s not on the list of approved types of tobacco, while nicotine pouches aren’t legal to import because they’re classed as pharmaceutical products (need an import license, which I believe is practically impossible to get for these things).
See these previous threads - the first one from me after having some confiscated by customs:
I do occasionally run into random Scandinavian people who bring it in with them when they arrive, but buying it locally or having it mailed in seems like pretty much a no-go now and for the foreseeable future (at least for me - customs have confiscated my orders twice now, so I’m probably on some list and haven’t attempted it since my thread above 
).
Maybe nicotine gum would be an acceptable (albeit inferior) alternative if you need the fix. Some pharmacies really overcharge for it, but it’s like NT$799 per box at the Shanghai Union Dispensary near Ximen/NTUH (cheapest place I found when I was using it, though haven’t needed it for a few months).