Because your phone is old or from a recent Damus update?
Discussion
I guess the battery got destroyed from all these months
it's an iPhone 12, so... old-ish?
All iPhones before 13 are terrible in battery health. My wife had 12 Pro. I have 13 Pro and she has 14 Pro now. The battery advancement after 12 is amazing and very noticeably improved. Time for an upgrade.
Or just change the battery 🤷♂️
You can get the battery replaced at Apple for about $90. So, if you’re happy with your phone you don’t have to get a new one.