So let's try and parse the joke that has been mentioned here. I disagree that you can't vivisect the frog. Cultural and literary analysis is a thing, a skill which helps us to understand ourselves and the artefacts of our culture. If you're all "ugh, it's just a joke" then you might not want to read this post.
(But also, please know you're living the unexamined life, and are no better than an animal. That was a joke. Or was it?)
RG had a joke setting up the idea of a celebrity; someone a bit like himself but morally bankrupt, self obsessed, self congratulatory. This person would be so self indulgent they would force a "kind gesture" on a child with cancer, come in with inappropriate tone and content, notice things about the person that make them different from "the norm" (i.e. no hair) and point that out with a huge lack of awareness. Gervais acts that person and says what they would have said.
That's a funny premise (and very similar to his excellent and monstrous creation in The Office). Lots of history for this kind of humour, lots of characters where it's funny that we see them saying, with no filter, things that we might think and have to check ourselves (That person is fatter than average, that person has less hair than average, that person is of a different race than me, blah blah).
The humour comes from a presumed emotional "embarrassing hot spot" in our culture. It assumes that we are all secretly thinking "Oh look, the main characteristic of that person is that they are black, or have a visible disability, that is Not Normal, and the majority of us in this room are white and able bodied, which feels Normal. Oh! but I mustn't say that, although it's true- because I might offend or upset them!!" It is very funny watching people struggling not to say inappropriate things that we all also struggle with. So I suspect that is where the humour lies; we have a release of tension laughing at someone who doesn't have the self awareness to hide their embarrassing inner monologue.
But! I don't personally find that a funny or relevant insight when it comes to the issue of "noticing difference". Most of us are streets ahead of that weird embarrassment now (oh no I mustn't mention the wheelchair!) It was on its way out with Basil Fawlty's Don't Mention the War, 50 years ago.
The idea of being "Woke" would genuinely be to think "Ah, interesting, I noticed some minority trait in a person before I noticed other things about them - what does that say about me? I'll just naturally refocus on other things and use it as an internal small reminder that we are all different." No shame, no embarrassment, just a bit of ongoing work we all do every day.
I think the cancer=bald head joke drags us back to an era we have left, where noticing difference for the majority of people was a big shock and suddenly a tedious thing you had to "pretend to not find unusual" - unless you were among friends when you could go back to your jokes about untrustworthy other races, hysterical women, etc.
So the joke allows RG to have his cake and eat it, by giving the audience that illicit thrill of laughing at people different from them while pretending they're not doing. It dog whistles to white, able bodied, "majority" folks who see the new way of ongoing work for diversity as an imposition on their inner monologue.
The people in the audience aren't laughing because children with cancer are bald. They're laughing at the idea of "a man who notices that about children who've had cancer treatment, characterises and simplifies them to their illness, and can't resist saying so". The trouble is, there is no way that character is funny (rather than distasteful) - unless you have a flicker of sharing the mentality (oh mustn't mention the bald head!). Otherwise how do you recognise it and find it funny??
I think folks who are in that place are a bit unevolved and old fashioned and it looks like Gervais is too. Maybe he's sending up people laughing at people who are like the imaginary celebrity. But I've seen no evidence of that in any discussion he has done about his work. And indeed if he is, he is mean spiritedly laughing at his own audience as they aren't in on the joke.
Thanks for coming to my TED talk :)