It’s not like a battery is soldered there, you can still replace it and it’ll cost you much less than getting a new phone. AFAIK I can still get a new battery on my iPhone 7 which is 4.5 years old.
https://www.ifixit.com/Guide/iPhone+12+Battery+Replacement/1...
And you just can’t buy original battery, they’re available only to selected service centres.
Currently it takes an hour at most to do at any repair shop. It's good enough. What matters is that it's possible for a reasonable price.