I don’t know what tips you have been following, but most of what you see on the Internet is wrong. The absolute best way to slow the decline of battery capacity long term is to enable Optimized Battery Charging (Settings/Battery/Battery Health) and charge the device overnight, every night. The battery will fast charge to 80%, then pause. During the nighttime pause the phone will use mains power instead of battery power, allowing the battery to “rest”, and thus reducing the need to charge the battery quite as often. The phone will resume charging to reach 100% when you are ready to use your phone; it will “learn” your usage pattern. If you enable iCloud Backup (Settings/[your name]/iCloud - iCloud Backup) the phone will back up overnight also, assuring that you can never lose more than the current day’s updates.
Any “tip” that says to disconnect the charger before the battery reaches full charge essentially guarantees that all energy to run the phone will come from the battery, and never from an external source. The battery charge will go up and down constantly between charging and discharging, never “resting”. So naturally, as it is predominantly charging and discharging that has a negative effect on capacity any such strategy is not optimum.