I noticed my 2014 MBP had two screws pop off the bottom because of swelling. I opened it up and oh boy, half the cells were puffy.
I disconnected it and removed the battery (Apple stores will take them to recycle).
I ran Geekbench 5 with the battery out and here are comparison scores. The 1st is with battery out, and 3 and 4 are battery in. The system is usable but noticeably crippled. Apple does this because the battery is used for any power demands over what the PSU can supply.
If you rather do it yourself, a battery and tools are less the $100. I'm waiting on a battery delivery now.