Returning to the retail version of the game after a 1-year layoff. Desktop running Win 11 on an Asus ROG Strix X570-E MB w/ Radeon RTX 2060. After doing all the game updates, my addons were broken (no surprise there). So, I renamed and moved my old WTF, interface and cache directories. Did a “scan and repair” as noted by more than a few other posts on the forums. Then installed Atlas (just the base app) using my account on CurseForge. Upon loading WoW, the addons page still shows a big, red “?” next to Altas - only addon I’ve added since cleaning out folders and scan/repair and it says it is out-of-date (load anyway). It seems to work in game, but is there an issue I am not aware of? A step I missed in the process? Would like to install other addons but not sure if it is going to be a problem.
Did they have a version for the last patch? Reinstalling a mod if it’s not updated for the patch wouldn’t work.
Last version I found was for 10.0.7, you can choose to load outdated add-ons, but the client is 10.1, hence the warning. If you want to make sure, download nis versions that support 10.1
Not every author will update their addons to the new .toc version if it isn’t broken.
That and even if an addon has been abandoned by the author it may work for years as out-of-date until Blizzard breaks something the addon uses.
The addons .toc version and the game clients .toc version are the only comparison that decide it the out-of-date flag is shown (it doesn’t do a code check).
Wonderful, quick replies! Thank you. Their author has abandoned none of the addons I want to install. Atlas only shows an updated version to 10.0.7. Not all addon authors are quick to update their addons with each new patch. So I installed Handynotes, which does have a 10.1.0 version which still shows a red “?” but is not listed as out-of-date. I will ignore the red “?” mark, as that may merely be a graphical issue. Thanks again for the kind and informative responses. 
The red ? is for an addon icon (an option added in 10.1). If an author hasn’t assigned an icon you get the ?. It has nothing to do with being out-of-date, only the text.
Thank you, Fizzlemizz. Good to know.