Iron Brigade

I know the game and played many hours through the campaign with some mates with the"games for Windows Live" or maybe a Steam version back in January 2013.  It was only about $10 back then and I picked it up with some Steam bundle sale. I didn't give it much thought, believing it to be one of those complex war games with a high learning curve. 
 I'd never heard of it but a few of the lads had picked it up and we thought we'd give it a go. 
It was original, very simple gameplay and an absolute blast, literally and figuratively.  Sort of a Co-op battle arena campaign with single person "mobile trenches" which resemble giant robots(think battletech) versus the aliens invaders. There was a reward system The Mechs could be retrofitted and upgraded with various random loots taken from enemy corpses and I think there was rewards at various experience levels too there was quite a lot of variety in that department.  If I remember correctly there were lots of statistics as well which added some depth.  

I thought I played it also on XBOX one as a single player game and ran through the campaign but it's not reflected in my achievements. 

I can't answer your question since I don't know if I own the game on XBOX and It left XBOX game pass mid last year. Oddly leaving game past happened just after Microsoft acquired the development studio who are now part of XBOX game studios, . I would have thought, the demand for the game was there and now solely owned by Microsoft that Double Fine would have a sequel  in the making. I'm not really sure why Microsoft bought them though, clearly, it wasn't to drive an Iron Brigade franchise. 

I digress from your question though, sorry. ADD and all that attention deficit stuff. 

Back on topic....

I don't know whether people still play it.  

From what I can gather, they never got multiplayer working stably with the XBOX one "backward compatibility" version. 
 This  or this thread suggests that there were multiplayer stability issues which existed from around 2015 which were not resolved by 2019.  
The Official Forums are dead: forums.doublefine.com/forum/12-iron-brigade/

It may be "supported" but, I doubt there will be many players and if stability is a problem, the experience will be fraught with disappointment. 

I don't think it was marketed all that well originally by MS but surely, there's there's money to be had in the franchise with a remastered edition or sequel. We can hope....