There's "flow" and there's FLOW. Even at minor levels of "flow", when you're still trying to "get in", you're building large mental models of the domain you're working in. If you don't have to build large mental models, then you can deal with interruptions easier - but if you spent the last 1/2 an hour getting your head into something and then some muppet interrupts you - poof - it starts crumbling, and if it's an interruption that lasts more than a few seconds, it quickly tumbles down into dust, to be rebuilt later.

There's a theory about mental exhaustion vs interruptions that I've definitely experienced - interrupt me or another dev enough and you can forget anything useful coming out today. Every time is harder to get back into after an interruption on a day, as your brain is getting primed to respond to external stimulus over internal thought.

Perhaps OP hasn't been challenged with a gnarly enough domain. Perhaps OP is lucky enough to have a well-defined domain they can TDD out every time (I found TDD to be a great remedy against distraction, because I can always write the name of the next test before leaving my desk to jolt me back to where I was when I get back - it's not perfect, but it's a vast improvement). But saying that flow state is overrated clearly indicates that they haven't experienced the smooth glide that is proper flow, getting shit done bit by bit, the right way, being able to effectively use multiple levels of "zoom" to look at the problem at different levels (which all rely on models built in your head).

I'll take a flowful day over "personal connection" with people who aren't actually my friends - they're just acquaintances: how much do you actually befriend people at your place of work (ie, actually do stuff with them outside of work, actively care about them like your long-standing friends, would take personal advice from them? On a regular basis? Tell them personal stuff? Who at your work really knows you?)? It was quite the eye-opener for me to realise that I'd been over-investing in work "friendships" with shitty people I don't care about and that I was just harming myself caring about them. You may be in the same boat and not even realise it until you think it over. Now I try to float above their turmoil, make things, do the best I can, and let their bullshit flow elsewhere.

Flow is actively harmful because it can lead to overwork?

Flow is bad because it's similar to deep focus seen in ADHD and Autism?

Give me a break.