How to remove stubborn adhesive residue from my windows?
Four years ? Your arm must be very tired and muscular. How did you find time to google forever?
Try DuckDuckGo.
You need a razor window/glass scraper.

Use the scraper and some denatured alcohol, apply a little denatured alcohol before hand to soften it up then scrape it and  wipe with the denatured alcohol, Repeat.
You may need to CAREFULLY clean the blade with some denatured alcohol between scrapings.