Use webp
Twitter serves webp's on most media types by simply adding the URL parameter format=webp. Since it is a vastly superior image format to jpeg and file sizes are significantly smaller, nitter should consider serving those for "small" images on tweets.

Simply adding the mentioned parameter here lowers the network usage through images in my feed from ~2.21MiB to ~852KiB https://github.com/zedeus/nitter/blob/5f31e86e0e8578377fa7d5aeb9631bbb2d35ef1e/src/views/tweet.nim#L64

Note that this isn't a portable solution since not all browsers, notably Safari, doesn't support webp unconditionally.