I’m a battery hobbyist, so have read through this, and other credible and corroborating research data. Looks like politics hasn’t changed.
We can look at the same 2 pieces of data (there’s more, of course) and still come to opposite conclusions. My read is that cycling off zero (to whatever % is convenient) is the least stressful for batts. However, a 2nd plug-in/day is inconvenient so I personally won’t go to zero, but my phone sees 8% way more than 80%.
IMHO, the keep-it-over-40% thing comes from infrequent use gadgets like a cameras. In longer-term storage a low low voltage Li-ion risks self-discharging below critical minimums - but that’s not a risk for daily use devices like phones.
‘The science’ actually indicates that 100% is the most significant stress factor, even over
120F heat. Apple’s ‘Optimization’ takes 3sec to flip on, while a ‘custom optimization’ takes ~10 $/min (smartplug + shortcut) - otherwise no difference day-to-day, just plug-in once/day and forget if you want. IME, that’s a pretty easy way to double life (I get/expect 6-7yrs service life).
That said, this is unpopular opinion, and most folks rather stick with conventional wisdom and the popular anecdotal info. But the ‘science’ and especially tools (iOS13 2yrs ago) are out there making it easy/painless… if done right.