Question: if the boy stops taking pb (cause they are tots safe and reversible, amirite), will he get his libido back? I assume he can use topical testosterone for penis growth (was suggested to Jazz Jennings), but what about “brain part” of sexuality? Is it gone forever?
Nobody knows. Nobody's ever given a child puberty blockers long term and then tried to make them stop and go through normal puberty before, as far as I know (or if they have, it's only just started happening). All the puberty blocked detransitioners seemingly started on cross-sex hormones, and I'd assume this person is also on HRT, which is complicating matters - they're not just coming off lupron.
There's a general axiom in brain development - "use it or lose it". Synaptic pruning gets rid of various connections in your brain while strengthening others and when it's gone, it's gone. On the other hand, how much of arousal is a physiological response rather than cognitive? We know chemical (or literal) castration of men kills the libido and sex drive. Is it possible that putting this person on testosterone might enable them to experience sexual arousal and find people sexually attractive? We just don't know.
Don’t pooners generally develop more aggressive libidos after being on testosterone for a while? I imagine a man finally going through puberty after having blocked it in childhood would get some of that effect too. No doubt it’ll stunt his development to have puberty without all the growth hormone you normally would have at that time though.
Pooners who've had a conventional female puberty absolutely will experience aggressive libido on testosterone, but it appears puberty blocked pooners do not - hence the Keira Bell case, where she's suing the NHS and is unable to experience any sexual function. Female and male puberty and sexuality are physiologically different though, so it's not 1:1.
I guess the point is moot. This isn't a kid who's trying to detransition after being puberty blocked to age 20. They're very much still wanting to be a woman, just a woman with sexual function and an amhole that isn't made from colon. Much like Jazz, they'd probably refuse to consider going through male puberty for a few years or even attempting the topical testosterone route.
It's where the terminally online trans approach to biology falls down - human beings aren't plug-and-play devices. It doesn't seem possible for someone to block puberty to avoid the "dysphoria triggering" masculinising changes while still experiencing the aspects of puberty that lead to normal male sexual function. The thing that makes the genitals grow into something big enough to be butchered into an amhole is the thing they were specifically blocking (in fact, in normal puberty, the testicles grow in first before any penis growth happens, and they specifically don't want the testicles to mature because they'll start producing testosterone that causes masculising changes - and blocking that testosterone will block the penis growth, because penis growth is obviously a masculising change). There's not really any way around it.
The dad's an idiot for not thinking this through, but the entire medical establishment have been force-feeding him information that puberty blockers are what his child needs, because forcing the kid through normal puberty will result in the kid committing suicide. It doesn't help that this is also echo'd in all the places he'd go for support -

"Although you spent years saving up for this surgery, you just need to spend
more money to go to specific surgeons! Here's some experimental procedures that will totally result in the nerves waking up!"
Amidst it all, a lone voice of honesty:

This was from 2017, btw. The whole thing is even more batshit now, although at least medical establishments are starting to admit the problems with puberty blockers.
This entire segment to me symbolizes just how much of a narcissistic episode this entire situation is. The guy has main character syndrome, so every little tiny thing must revolve around him. He wanted to live that fantasy of surprising everyone with how much of a pwetty gorl he became overnight NOW NOW NOW, and the fact that Bethesda's systems didn't work to instantly gratify him made his whole world fall apart.
One of the other points that's touched upon in his four hour screed is that he wasn't able to do any environment design on the video game he was working on. This was a fun job and it means you get to leave your mark on the final product, but although his colleagues got to do it, he was blocked from doing it.
While he characterises this as transgender victimisation, it's pretty clear that the boss needed him to finish his actual work, and his histrionics meant that work was not getting done so he didn't get a chance to have a go on environment design. I assume he was hoping being trans would mean he could skip the drudge work and only get to do fun things as the only Stunning and Brave employee in the department.
Also worth noting that he failed his performance review and was on his way out the door. Corporate HR offered him a deal where if he agreed to resign and sign a settlement agreement that waived his right to sue for discrimination, they'd pay for all his surgery (whereas if he'd been fired, he'd have lost his medical coverage for his scheduled surgeries). He actually accepted that deal, waited to have this surgery and
now dropped the YouTube video (which is why he's doing this instead of suing them for discrimination).
He does appear to be taking some legal action against Zenimax and AP Benefit Advisors LLC but it's unclear on what grounds (presumably "you held my surgery hostage to force me to sign a settlement agreement", when there was no obligation for them to offer covering the cost of those surgeries if he left/was fired).