u/Bug0221

This is a question i've always had, I always struggle with file sizes and the abysmal size limit on desktop but on mobile i can send larger pics and vids like nothing, like i'll take a pic with my phone and send it to a server/dm but when i copy and paste the same image on desktop it suddenly is too big to send, but then when i open and download it it's small enough to send, how does this work? Do mobile and desktop have different file size caps or what