On my S9+, I was able to send and recieve MMS on Wifi only without using mobile data. After I upgraded to the Note 10+, I'm no longer able to send MMS on wifi. I have to use my data. Please bring back this feature with the next update!
You need to have wifi-calling On if you want to send MMS over wifi. If the phone doesnt have wifi-calling on the network it will send via Mobile data. This except for verizon network since they use verzion messages app that can be send via wifi even no wifi-calling.