He is very nice to women, which is why he has never had a girlfriend and women do not respect him.

Ah, the perfect "cover" and ideal way to avoid gold diggers.

I have learned that he is very wealthy because being an awkward beta incel means women never date him which means he spends his weekends playing video games in his mother's basement and invests all his salary, so he is very wealthy.

Meh sounds to me like he's a "herbivore" type of MGTOW.

And how do you know he's an incel or even "celibate"? Have you been stalking him? Spying on him 24 x 7 x 365?

Who knows... maybe he has a sex doll at home? Maybe he hires an "escort" a couple of times a year? Maybe he just has better/more "control" over his sex drive than you do?

My fear is that this incel still wants women.

Why is THIS your fear? Why is this your business in any way shape or form?

Do you have the gay "hots" for him or something? (And I do not mean that as a "shaming" thing... but as an actual serious {but rhetorical*} question.)

* Meaning a question for you to ask YOURSELF... no point in replying here; as any answer you give to others will not be reliable anyway.

He is not a MGTOW

Actually there is really no way for you to know that for certain.

At least not at this point and from the apparently superficial & circumstantial tidbits of "anecdote" you've noted. Again he might just be very good at playing the "beta incel" part as a cover for being MGTOW (it is after all a more or less "ideal" one, the best form of camouflage is to hide in plain sight... to be so boringly predictable that no one {or at least no "normies"} given him any thought whatsoever -- moreover that isn't simply a MGTOW thing, it's a "Millionaire Next Door" thing, and a long-standing tactic of "tradecraft"** that has its roots in hunting/stalking).

And he may simply KNOW enough (perhaps better than you) to NOT talk about "Fight Club."

** Most people really don't seem to comprehend that the whole array of unique "trademark" characteristics of the "James Bond" style "world famous spy" (LOL, famous AS a "spy") ... are the exact opposite of what any actual "spy" or undercover agent would do; Ian Fleming's character was intentionally crafted as a farcical parody (i.e. what no real "spy" would do); so all "parodies" of Bond (Austin Powers et al) are actually farcical parodies of a farcical parody (that's the joke within the joke).

If it gets out that he is a cashed up incel, some post wall woman will take advantage of him

Maybe... or maybe not. Maybe he's not as ignorant and foolish as you seem to believe.

Not everyone follows the same "style" of being a MGTOW you know.

Hells bells, you've apparently missed out on your homework -- but we often discuss that kind of thing in various threads here -- rather than making yourself a "target" for HR/SJW types by being openly "MGTOW" (and risking "shitting" where you "eat"), it's often far more advantageous to simply "play along" in one form or another: some guys play at being a sort of (somewhat "creepy" off-putting) "playboy-flirt" (works especially well if you're NOT "swole"); others deflect attention become "invisible" to women and get automatically "friendzoned" by simply playing at being the "really NICE guy."

The open, outward, publicly "DGAF" type of MGTOW is not the image/style that most young "working" guys should be playing at in their workplace -- THAT type of thing is probably really best left to those who already have achieved financial independence, and both reach an age/stage in life where their resources are fairly strongly INSULATED against "attack" by anyone, whether employer, client or family & "friends" (i.e. they're in a true "Fuck You Position" -- and where awareness that they are MGTOW {or a "confirmed bachelor"} will be greeted by a "Yeah, Duh! We already know THAT!" by everyone in his life).

so how can I protect this man

What makes you think this is your job?

Seriously.