This is all anecdotal, so take it as you will. At some point in the past I used to be careful to do 80–20, or even 70–30 when possible. It was usually a pain, because I didn't get the full benefit of the battery, and I was always worried I might go above or below my targets. I still had to replace a battery after 2 years.
Then, with my previous phone, I decided not to worry about that and just charge whenever. The vast majority of the time I charged to 100% using fast charge, albeit not overnight. I had that phone for 4 years and it was only in the last year that I felt the battery had got worse. That last year was also after a big software update.
With my current phone, I'm doing 80–20 again—but more often 85–35—without fast charging. A year and half in and the battery has definitely degraded. I have easy access to a charger most of the time, and I use a software feature on the phone to limit charging to 85%, so my current schedule is easy to keep to, but if it wasn't, it probably wouldn't be worth it for me. I'd just accept that, worst case, I have to buy a $50 battery every couple of years to not have to worry about charge levels.