Typing anything in another window that is not my browser
Which windows exactly? The apps you're typing things into might be spying on you.
M$ and their 738 parters really value your privacy, so if you're typing things into Excel...
copypasting the words "trans" and "talking"
What applications were running on your computer while you did this? Any of them could be recording clipboard history; it requires no special privilege.
Heck, I wouldn't be surprised if Windows itself was recording this and sent it to daddy M$ to train LLMs and maybe sell it as a little multi-billion side hustle.
transgender videos about "How to change your voice" start popping up in my feed. Please know I have zero interest in transgender politics/culture/anything, it is not something I have ever searched for or engaged in online.
Maybe Google knows something you don't? JK.
A more plausible explanation is that Google knows that you're in the Fediverse (ever Googled it?) which has a far above average concentration of queer people.
What is also plausible is that someone living with you (i.e. your family) or a friend is trans and you're obviously associated with them.
Google doesn't recommend queer content because they think you're queer but because it's what their data-defined statistical algorithms (""AI"") predicts you are likely to be interested in and therefore watch ads for. If you know a queer person or are often in contact with them, you are simply quite a bit more likely to be interested in queer people than the average and therefore more likely to click on queer content.
Possible that Youtube is reading my clipboard? Reading my keystrokes?
Youtube itself? Near impossible.
Other applications? Possible but likelihood unknown.
Listening to an album via VLC, while Youtube is open in my browser. Suddenly, more tracks from that album start showing up in my suggested feed. Possible Youtube is reading the titles of other apps current open on my machine? (VLC changes its active title to the name of whatever file is currently open)
Again, Youtube itself directly isn't doing anything like this. If that album is related to what you were listening to on YT or is even simply also popular with people who listed to the same things on YT as you do or are just generally similar to your person; that's all it takes for YT to attempt to show it to you.
Also note again that any application on your Windows or Linux PC can read the window titles of any other application or even simply scan your media library or other files.
Discord does this for instance for their rich presence function for instance and I would again not be surprised if there was a little multi-billion side-hustle going on.
I use Youtube all the time as my personal version of Spotify.
If you're not reliant on YT's recommendations, I'd recommend you to download the songs you want to listen to and listen to them on a local player.