that is true!

Samsung apparently set their 100% charge point middle of the road, a compromise between battery longevity and runtime. I charged my older Huawei P9 up to 100% all the time, the capacity of that dropped hugely in two years, but AccuBattery won't work on that phone. Charging the Pixel 4a to 80% it's still going well, though runtime is decreasing slowly, but I do keep installing more apps.

I've added links to additional, newer research to the first post of the thread.

Oblivian: My find X3 lite has built in smarts since 11
Huawei are quite aggressive. Removes apps permission etc
Recognised I get up about 7. Now pops up it will optimise charge to be ready at 7. But doesn't float or ramp fast
Plug in during day and it goes super charge.
Presumably absorbed a 3rd party app and integrated.

Yeah, similar to sister company OnePlus: I have a 7 Pro and it charges to 80% then stops until 5:30am or so when it resumes and finishes at 100% as I wake up. Seems to work well.

I've automated turning off the USB charger once battery hits 80% using a Home Assistant automation, the Home Assistant Android App (which reports battery info), and an Athom smart plug (which cost $33 for two, but not sure which currency, AU or USA).

alias: Phone stop charging at 80%
trigger:
  - platform: numeric_state
    entity_id: sensor.phone_battery_level
    above: 79
condition:
  - condition: state
    entity_id: switch.athom_plug
    state: "on"
    for:
      hours: 0
      minutes: 0
      seconds: 5
  - condition: state
    entity_id: binary_sensor.phone_is_charging
    state: "on"
  - condition: numeric_state
    entity_id: sensor.athom_plug_power
    above: 0.8
action:
  - type: turn_off
    device_id: (removed)
    entity_id: switch.athom_plug
    domain: switch
  - service: notify.myemailservice
    data:
      message: Phone is charged! Power has been disconnected from the charger.
      title: Phone is charged!
mode: single

Some people replace phones frequently, so the battery lifetime wouldn't be a big deal for them. Others hold onto a phone until it fails, for them it does matter.

Xiaomi A1 which is five years old. Charged 100% every night with no precautions taken. Original battery now at 80% health (2468 mAh), which is still adequate to last a normal day.

So my experience is any benefit is marginal at best and does not justify any effort. I am satisfied 5+ years of life for a mid-range phone. I accept other's experiences with different brands may vary.

And even if your battery life is now bad but the phone justifies continued usage... you can replace your battery fairly inexpensively.

Interesting, Stu. You may have gotten lucky with a battery that good, my last phone degraded much more quickly to the point that after 2-3 years it had to be charged during the day a least once. Each manufacturer sets the 100% level, it could be Xiaomi sets it lower than others.