Letting the battery level go down below 20% is not a good practice. This is the only precaution you should always keep in mind and respect it, if possible.
Modern Li-Ion batteries can be charged whenever you want and how long you want (no overcharging problem, since iPhone stops automatically charging when the battery reaches 100%).
I have your same configuration: XR running iOS 12.4, and I'm using iPhones since 2008 (3g), charging them overnight, everynight (even if the battery is 90%), and my batteries have always lasted more than 2.5 years.
Lifespan is measured in charging "cycles", and all iphones can support easily 500 cycles.
1 cycle = charge from 0 to 100%
1/3 cycle = charge from 75 to 100%
1/2 cycle = charge from 50 to 100%, and so on.
That being said, I do not use Telegram, so I can't judge it, but I would assume that all apps, if used at 1% battery level, could have unpredictable behaviors when a peak performance is needed.
That's my opinion.
Giulio