If you have Software Mode enabled, then the preferences for AUR will not show. Once you disable it, then when you open again preferences the AUR options will show.
Regarding the update of AUR packages … If from terminal with this command
pamac checkupdates -a
you get some package as
Out of Date:
package-name XYZ.1.version-2 AUR
then make sure to check that package AUR page and see if is Flagged as Out of Date. If that is the case, then there will be no update for it, unless the packager will update it … I hope this makes sense and i’m not equivocating.