In the short run, no. In the long run, yes.
When lithium batteries are kept between 80% to 100% for extended periods of time, they begin to degrade.. it doesn’t happen right away but over a period of time, it does. Remember the last smartphone you had? Remember how the battery used to be very good but later on, it doesn’t hold a charge very well? So if you kept it above 80% for a long time, that degrades the battery… so keeping it plugged in at 100% is not good for the battery.. if you charge the battery to 100%, you must immediately use the battery right away and not keep it at 100% for too long.
Keep in mind, Apple has addressed this issue with degrading batteries so with iOS 13 and above, they have a new “optimized battery charging” feature which automatically stops the charging to 80%, and then it charges to 100% about 30 minutes before you usually unplug the charger (it learns from your daily charging habits). This feature is already enabled by default (you can check the battery settings)… but if you really want to protect the battery, never charge the phone overnight and charge the phone during the daytime when you can monitor it.. and manually unplug the charger before it goes past 80% charge. If you do this, your iPhone battery will last many, many more years… otherwise you can pay Apple $69 for a battery replacement (plus appointment fees and such).
Even Tesla cars have a feature where it stops charging at 80% to prolong the life of the battery.. because replacing the Tesla car battery is very expensive.