How much would I gain from upgrading my Nikon D5100 to a Fujifilm X-T4?

I’m currently still using my very first DSLR, a Nikon D5100 which I bought nine years ago. The camera is still working well but I’ve been thinking about upgrading it lately for mainly the following reasons: The low-light capabilities are not that great. I find that at ISO 800 it already degrade…