Apple's near-adoption of NeuralHash.
For years I was comfortable with using big tech companies that had strong tech credentials and a level of trust in the community for implementing things well, securely, and in a way that preserves privacy and respect for the user. Closed systems provided by them were therefore trustworthy to me, having faith that the world-class security professionals and software developers and product owners were all implementing things well, even though I had only limited direct visibility of that. Apple in particular had a reputation for having the most respect for users and their privacy.
Then NeuralHash broke the spell for me. I had an epiphany, a sudden realisation that the untrustworthiness I knew existed in other companies existed in these ones too. I switched to a firm belief that if it's possible for a company to do something naughty with your data, then on a long enough timeline it's inevitable that they will.
I resolved then to avoid big tech wherever I can, and where I can't I try to implement things in a way such that it isn't ever possible for them to do nasty things with my stuff. I've de-Googled, de-Appled, and de-Amazoned, and returned to having a strong emphasis on managing my privacy and taking ownership of as much of what I use as I can.
I'm with you. I hosted my own mail server for about five years before giving up, and it irritates me when folks say it's not that bad.
Even with perfect DKIM and DMARC configurations, spam filter lists would add me silently and repeatedly, and I'd frequently have to go through their processes to remove my domain. Then Google would sometimes start treating me as spam too, or outright deny email delivery, requiring some tweak or another to enable delivery.
It was a constant battle, one in which you don't always know when you're losing since nobody reaches out to tell you when you've been blocked. It was exhausting.
Giving up and moving to Proton was a sad moment. I really wanted to stay as limited as possible in my dependence on other tech companies, but email just wasn't reasonable for me at all.