This page says battery is "built-in," which does not bode well.
Repair guides and disassembly information for the 16-inch MacBook Pro released in October of 2021, featuring Apple-designed M1 Pro and M1 Max SoCs. Model A2485.
www.ifixit.com
By easily replaceable, I meant able to get in and out to replace a battery in less than 10 minutes, like on my old 2009 MBP, not having to break down the whole inner architecture AND dissolve adhesive, like on some of the retinas.