After a long time of users asking, Valve has actually added an official Battery Charge Limit setting in the latest Steam Deck Beta update so you no longer need to use third-party tools.
TL;DR: Mostly screws, but the battery itself is adhered in with several adhesive strips. Be careful if you follow this guide at home as using too much heat can damage the device and/or the battery.
In summary: No, it’s not that easy to replace. As someone who fixes a lot of electronics I hate this practice of adhering batteries (much less anything replaceable) into a device.
The iFixit Guide to replace the battery on an Steam Deck (OLED)
TL;DR: Mostly screws, but the battery itself is adhered in with several adhesive strips. Be careful if you follow this guide at home as using too much heat can damage the device and/or the battery.
In summary: No, it’s not that easy to replace. As someone who fixes a lot of electronics I hate this practice of adhering batteries (much less anything replaceable) into a device.