Here's a look inside one of the backstage rooms on the set of "Today" ... which Caitlin O'Connor posted on her social media account Monday showing support at Joe's appearance-- this as Joe was plugging his new "Deal or No Deal Island" show, on which he's the host.

Anyway ... here's a glimpse of what 'Today' looks like behind the scenes for talent and friends of talent. We're told this is a makeup room there -- so, not necessarily a dressing room, it seems, but probably pretty close. That jibes with what we've heard about these rooms ... namely, they kinda suck -- which is proven here in the bare-bones environment COC's in.

Worth noting ... we're told Joe was in a different room than the one Caitlin posted from -- so, unclear if it was worse or better than this. Based on what we've heard about Kelly's walk-out, it probably ain't much better ... and that's saying something based on what we see here.

Based on Caitlin's photos, the makeup room doesn't look all that glamorous ... and it comes off as cramped. There's a chair, bulletin board, and some storage units and that seems to be it, at least going off what's in the frame.

As you know, the 'Today' makeup and dressing rooms are under the microscope because Kelly stormed off the set earlier this month, a result of what her team says were issues and complaints with her dressing room.

Kelly has pretty much refused to talk about the incident, which is why folks are still interested in what went down.

Bethenny Frankel's already ripped Kelly for being a drama queen ... she says it's no secret the dressing rooms at 'Today' aren't super glamorous, and she showed them off in an earlier video. According to Bethenny -- this is something that comes with working on 'Today.'

Now, we're getting a different angle from Joe's GF ... and it doesn't look all that better, TBH.