why is imessages so slow on macos

its always been an issue for me as I've never had good sync between my imessages between macos, ipados, and ios. i turned on the imessages sync but it never works. i get a lot of spam messages too and i delete those frequently on my phone but it appears unread on my mac (if u know how to get rid of spam permanently, pls tell me). can anyone help me figure this out?