I got you fam.
First, install a browser extension that can execute user scripts, like "Tampermonkey": https://chrome.google.com/webstore/detail/tampermonkey/dhdgffkkebhmkfjojejmpbldmpobfkfo
Then install this user script that auto-expands all images on lemmy: https://greasyfork.org/en/scripts/468868-lemmy-image-expand
Sometimes the script does not work if you use "Next" or "Previous" to switch between pages. In this case you need to reload the page.