I tried these urls to block on the router and it worked very well.
v19.tiktokcdn.com
v16.tiktokcdn.com
api.tiktokv.com
api-h2.tiktokv.com
api21-h2.tiktokv.com
mon.tiktokv.com
ib.tiktokv.com
p16-tiktokcdn-com.akamaized.net
v16-tiktokcdn-com.akamaized.net