I mean, it's telling you to update the Address Library mod. If Fallout 4 gets an update, it may take them a bit, but they should roll it out.
https://www.nexusmods.com/fallout4/mods/47327
You probably want the current version of that. If Fallout 4 just updated, then you may need to way for it to be updated.
That thing is required to know where in memory other mods need to fiddle to do stuff outside of the APIs that Bethesda provides, so it's extremely dependent on the version of Fallout 4
basically, it being updated means that all the other mods can rely on it knowing what the relevant addresses are and don't have to be updated themselves. If Fallout 4 gets updated, you're probably going to need to update it.
EDIT: Some people who run heavily-modded Fallout just buy the thing via GOG to avoid Steam pushing updates entirely, so that they don't have a window where an update comes out but relevant mods haven't been updated. You can prevent Steam from doing updates via breaking the update mechanism, but as of 2026, Steam normally updates games automatically, and GOG's mode of operation is to only update manually.
My own view is that the real issue is that Bethesda really should (a) expose some of the stuff that Address Library provides via supported APIs to mods, so that Address Library isn't necessary, and (b) should use Steam's beta branch functionality to establish a "stable" branch for people running mods to have an option for. Not really what Steam intends the feature for, but there isn't really a better way to both permit updates and deal with the "mod authors need time to update their mods" issue in 2026 in Steam.
EDIT2: I don't think that you can directly blame Bethesda for Fallout 4 updates breaking compatibility there, aside from maybe not providing APIs for some stuff that mods would like to do so that they don't need Address Library. Address Library is twiddling values in memory. It'd be unreasonable for Bethesda to commit to having a fixed memory layout across versions; no game developer is likely going to do that.
