any decent board game/mario party style games for co-op on same machine

Pummel Party, perhaps.

The Jackbox Party Pack's?

I came across many, but can't name any of them.

Unfortunately none exactly like mario party, but here are some local co-op games that are fun enough:
Abraca
Boomerang Fu
Heave Ho
Lovers in a dangerous Spacetime
Key we
Marooners
Moving Out
Overcooked
No time to relax
Tools up
Totally reliable delivery service
Ultimate chicken horse

Maybe one of them would be fun?

Steam search is a pretty good resource. Here's a few searches, for example:

"Board Game" + "Shared/Split Screen PvP" = https://store.steampowered.com/search/?tags=1770&category2=37
"Board Game" + "Shared/Split Screen Co-op" = https://store.steampowered.com/search/?tags=1770&category2=39
"Board Game + Local Multiplayer" = https://store.steampowered.com/search/?tags=7368%2C1770
There will be overlap, but I thought I'd hit you with all three.

You can also just do a web search for "steam games like mario party" or similar.

I saw Pummel Party, Marooners, and Party Panic mentioned in multiple lists. Looks like it might be what you're looking for.

Here's a curator list I found: https://store.steampowered.com/curator/8485829-SvenEvils-Playground/list/43520/

I haven't played it, but is 100% Orange Juice like it? Looks a lot like it from the photos on the steam page.

Ticket to Ride. I have it on Epic (freebie) and I've played at least a few hundred times.
If young kids are involved and the game is a bit too complex for them at the beginning, then also Ticket to Ride: First Journey.
Edit: It's not simultaneous, but "change your seat" gameplay on 1 comp, if you don't want each other to see your cards. However, I think, you can play it both ways.
Generally, I would recommend checking Asmodee Digital games.

off the top of my head Stikbold!

Try Tabletopia on Steam (free) and search their website for games with Hotseat mode if you want to try some tabletop games. There're games with rounds as short as 5 minutes and as long as 5 hours.

root

I never played it, but if you want a rip-off, Mega Monster Party looks very similar.

Mario Party specifically? Only things I can think of off the top of my head are 100% Orange Juice and 200% Orange Juice.
Otherwise with boardgames you'll want anything from Tabletop Simulator to things like Armello, Catan, Ticket to Ride, 5D Chess (or almost any other chess game)...

Try playcloud party games if you enjoy the minigames aspect ( Scan QR & play using smartphones as controllers )
https://www.play-cloud.com/playcloudpartygamessimilar