Unfortunately not all mobile browsers will show the entirety of the alt text if it’s too long, Firefox Focus on Android 15 and this exact comic is a perfect example, for my screen it cuts off about 3/4 through the alt text. The mobile version ensures it’s all readable
https://xkcd.com/979/
https://m.xkcd.com/979/ <- Mobile version with alt text
Long pressing on the image also shows the alt text btw
Unfortunately not all mobile browsers will show the entirety of the alt text if it’s too long, Firefox Focus on Android 15 and this exact comic is a perfect example, for my screen it cuts off about 3/4 through the alt text. The mobile version ensures it’s all readable