This is a great doc. My own mother was becoming quite reactionary from fox news and trump speeches being recommended to her via the youtube algorithm, to the point where she started claim I had been brainwashed by the liberal media for trying to explain to her that climate change was real and advocating for helping homeless people.
When I was able to, I would try clicking the 'Not interested' or 'Don't recommend this channel' on those videos from her computer when she wasn't in the room, but it was always just recommend the same content from a different channel random channel, it was almost impossible to retrain the algorithm, and all it would take is her watching a few more videos for it to continue to recommend that stuff.
Like in the documentary, at some point she had an appointment to go somewhere and I happened to have an opportunity to access her computer for an extended amount of time.
What I did was subscribe her channel to a bunch of left-wing news sources, and more critically, I installed the browser addon BlockTube, which allows you to create a blacklist that seamlessly prevents videos or channels matching those keywords from displaying on youtube. I added words like Trump, Tucker Carlson, Elon Musk, Fox News, Sean Hannity, etc.
Like the father in the documentary, taking those negative sources away took effect almost immediately, and now a year later, she's almost a different person. No longer reactionary, no more pearl clutching about trans people, and now believes climate change is real (she took a liking to PBS Terra), I was even able to convince her to install solar panels on her house!
I was lucky that she isn't tech savvy at all, so that blocking addon will never be discovered. She also wasn't deeply invested in fox news or those talk show hosts, so never noticed that they stopped showing up in her feed, nor bothered to seek them out again specifically.
If anyone else has a parent like that, I would strongly suggest trying those two tactics if you ever get the chance.