Dead iPhone 7 - not turning on, not indicating charging

Hello all,

A few days ago my iPhone 7 suddenly stopped working, it won't turn on and doesn't respond to the charger connection, just blank screen. Until then the phone worked normally.

I last used the phone when it was almost dead (1% battery left) and suddenly a major lag appeared, so I turned off the screen and put the phone away assuming it was caused by low battery. By the time I got to the charger, the phone was completely out of battery. So I plugged it in to the charger and left it like that overnight, but in the morning I found that the phone was completely dead. Doesn't respond to charger connection, unable to turn on, unable to do a hard reboot, nothing just a blank screen and no output at all (not even the red battery icon or the Apple logo).

I've tried all the tips I could find - different chargers, different sockets, tried hard reboot (power button + volume down), tried to clean the lightning port but no result. The phone also doesn't show up in iTunes when connected to a Macbook.

Details of the iPhone at the time of the defect:

Model: iPhone 7 128GB, matte black

iOS 14.6

Age: 5.5 years (yes quite old)

Storage usage: 127 out of 128GB

Battery condition: 83% (in my opinion the indicator was stuck at this value, but actually it was less, the battery was around 2 years old)

Lightning port was a bit worn - it didn't "click" when plugging in the charger but charging always worked fine without having to move the charger around to get contact.

Does anyone have any tips or similar experience?

I'm planning to visit a repair shop, but before that I wanted to ask if there was a DIY solution.

Thank you in advance for your recommendations