And it's fucking superglued in. You have to use a heat gun to even have a chance of removing it, and Valve have acknowledged they may change it in the future as right now it is admittedly ridiculous.
So yes but technically no. It is not immediately user serviceable.
To replace the battery in the Steam Deck, you need to heat up the adhesive to allow the battery to be removed, which I believe would violate this directive. That said, it doesn't seem like it would be too difficult for Valve to make it a bit easier in the next Steam Deck and comply.
For the record, you don't have to take "everything else" out first. It's actually quite accessible once removing the Steam Deck back plate, which is easily done with a Phillips head screwdriver.
The bulk of the 2-4 hour estimate on iFixit is dealing with the battery adhesive.
(source: I've opened my Steam Deck to swap the SSD, and I just opened it to attempt a band-aid fix to the right bumper after dropping the Deck directly on it while waiting for the part to restock)
It's real great on Valve for helping furnish the parts and make it less difficult, the language passed reads as “with no tool, a tool or set of tools that is supplied with the product or spare part, or basic tools.”
Under that, Valve might already be fully compliant given that official parts are sold readily and the Deck can be opened up with basic tools. What's most wonderful about this is how it'll apply to phones.