Message about ink asorber full keeps appearing

When the printer is not being used, the print-heads slide to their "resting" position,
in order to keep the ink-jets moist, i.e., to NOT dry-out.

Some ink is absorbed into that INK-ABSORBER.

Now, after a few years of usage, that ink-absorber is "full".

Like taking-out the garbage from your kitchen waste-basket when it gets full, and replacing the full waste-basket with an empty waste-basket, it's time to get your printer serviced -- replace the "full" ink-absorber with an "empty" ink-absorber.

Note that CANON printers do not actually "measure" the fullness -- they electronically estimate the fullness, given information about how much you print, and how often you print, and the "density" of the pages that you do print (text is much less dense than colour-photos).