Roughly five months ago, I tried to connect to my friend's XboxOne server that I had been playing on with my Windows10 computer in the previous weeks. I got the error message "Could not Connect: Outdated Client." It appeared that we were in different versions, the pc version being ahead, so I thought we just need to wait until the XboxOne version updates. Well today, my friend's Xbox says that it's been at V1.4.5.70 since 11/6/2017 and I'm at V1.5.0.4, and we STILL cant play together. Even when I create a world he gets the same message.

I went troubleshooting a bit and found other people with the similar issue of the Outdated Client message. And all that anyone has said is to wait. Well? Where is the update for XboxOne??

I found somewhere that it may be related to being signed up for the beta content through the Xbox Insiders Hub. So I went into the hub and unsubscribed to it and tried to re-connect to his world. Didn't work. I then got my friend to sign up for the content to see if his client updates on the Xbox. Also didn't work.

So, am I doing something wrong? Is it really the issue that Mojang/Microsoft haven't updated one of their platforms since November of last year? Or am I missing the vital information on how to switch versions like in the Java edition on PC?

If there really isn't a way to switch your versions manually then there needs to be. This was an important feature in the Java Edition and I see no reason that it cannot also be in the cross platform edition.