What are some good Vpop groups today?  

I've been listening to a lot of Rhymastic as of late, and also Binz. But other than that, I'm still finding out about a lot of great Vpop artists. Check out the topic area for some more suggestions: 

Vpop Artists

I am more familiar with older bands like 365band. It is probably worth getting lost on YouTube to discover new music and bands!

Besides Monstar, here other V-pop groups that I would recommend :

365DABAND - BỐNG BỐNG BANG BANG | OFFICIAL MV (TẤM CÁM: CHUYỆN CHƯA KỂ OST) :

UNI5 | NÓI DỐI CẢ THẾ GIỚI VÌ EM | Official MV :

Take It Slow | LIME | Official Music :

Lip B | SỐ NHỌ (BAD LUCK) | Official MV 4K :

Here is a link that might interest you :

V-pop/Vietnamese pop groups for beginners :

https://forum.allkpop.com/thread/829-v-pop-vietnamese-pop-groups-for-beginners/

In Vietnam, usually, music groups are not as prominent and noticeable as solo singers. As far as I know, Monstar has officially disbanded and the members will be doing solo activities. But in the Vietnamese music market, there are still some talented groups. You can try.