I think folks are missing the point of what "mansplaining" means. There are equivalents related to racial privilege, straight privilege, class privilege, cis privilege, etc. as well. Basically it's where someone from a more privileged group undermines the experience or comments from someone in a less privileged group - basically "teaching granny to suck eggs." And yes, it's real. See it all the time on here, for example.
It's where a woman talks about the barriers she's had in her career due to gender discrimination and a man tries "splain" why her experience is bullshit - anything from, "you probably didn't have the aptitude of the men," to "most women don't want to put in the time and effort to get the promotion," or similar.
It's where a person of colour talks about being harassed by the police and a white person chimes in about the time a cop was a bit rude to him when he was caught speeding, or that it's probably just a coincidence and nothing do with racism, etc.
It's when a disabled person describes the negative impact of service cuts on them and how it's going to be impossible for them to keep their job and a non-disabled person "helpfully" suggests a whole list of different jobs they could probably do instead.
It's when a working class person describes how hard it is to make ends meet with their hours cut at work and everything costing more and a more privileged class person starts talking about how awful they had it when they were broke for a while at uni and had to eat beans on toast for a week.
And yes, someone of the same group can "splain" to others, particularly where they've "played the game" and think they are in a more advantageous position than the person they are talking to. Perhaps it helps them feel better about themselves if they can talk down to someone or maybe it's that they want to distance themselves as much as possible from the "undesirable identity" that they no longer want to occupy. Wevs.
Either you get the concept or you don't. Folks who like to splain generally don't get it, or make a big deal out of insisting that they don't get it (when they choose not to.) Methinks there could be quite a few such folk round these parts at the moment, sadly.