Very weird glitch happening on iPhone 6 Plus

[Cookiehead]

My iPhone 6 plus has been glitching and turning off randomly for a few days. When I turned it on today, the screen never came on. Eventually, I noticed it was flickering and it finally turned on and could be used normally.
Then, I noticed that my phone wasn't connected to WiFi, and the time was wrong...
I open settings, and the WiFi switch does nothing, Bluetooth is unavailable, and when going to General > Date and Time, it just freezes the Settings app. When going to General > Reset, it freezes as well. Also, in the About page, it says "Applications: 1"
What should I do?

 

[Adora]

Sounds like a bad hardware damage.

I have a 5s here, that also turns off suddenly if not permanently connected to power. But everything else works. So it's only the battery.

My iPad Pro from 2016 just stopped working too a few weeks ago. It suddenly was in a boot loop and since the battery is empty it doesn't charge anymore.

Edit: I bought a refurbished 8 Plus with 256GB for less than 150€ in April. Should be even cheaper now. Maybe you should do the same if the 6 Plus had been enough for you and you don't have much money. I don't think repair is worth it anymore.

 

[now i see it]

Either replace the battery or the phone. No guarantee that a new battery will help but iOS battery health reported for my iPhone 6 Plus is grossly incorrect. Mine says it’s still at 96% on the original 10 year old battery. Not possible