Replacing battery on Samsung phone

[BresciaBike]

I'm intending to find a phone repair shop to replace the battery on a Galaxy S21 as the battery isn't lasting very long. Phone is out of warranty. However, a friend told me that it is surprisingly hard to do/get done and I shouldn't bother. Has anyone replaced or had replaced the battery in their Samsung phone?

Bump to see if anyone has advice

My friends husband has a phone repair business. Not just Samsung - most modern phones, make DIY jobs hard (but not impossible). He can do it (he's very good) and most of the time it's ok - but he is very clear that it could damage the phone. Samsung do it themselves. So no, not impossible.