What problem does the feature request solve?
Frequently, users with larger modpacks returning after a period of time might not check through all of the mods they have downloaded, simply clicking "update" and continuing. While more proficient users might think to scroll through first and make sure everything is up-to-date, a number might not think to do this, leaving them with deprecated mods and needing to ask for help. Since this is a common problem pattern, implementing a solution in the mod manager might make sense.
Example mock-up (optional)

The first idea I had for this UI would be to have a banner pop-up similar to the "update all" pop-up. Clicking "disable all" would disable all deprecated mods in the user's modlist. While I can think of a few that this might cause some odd behaviors with (IntroSkip being deprecated but with a updated fix mod, for example) I think the number of problems this would solve might make it a worthwhile feature.
Additional information (optional)
Feature inspired by Chinchi's LogViewer and the utility of the "deprecated mods" feature.
What problem does the feature request solve?
Frequently, users with larger modpacks returning after a period of time might not check through all of the mods they have downloaded, simply clicking "update" and continuing. While more proficient users might think to scroll through first and make sure everything is up-to-date, a number might not think to do this, leaving them with deprecated mods and needing to ask for help. Since this is a common problem pattern, implementing a solution in the mod manager might make sense.
Example mock-up (optional)
Additional information (optional)
Feature inspired by Chinchi's LogViewer and the utility of the "deprecated mods" feature.