You asked
Should I upgrade from the fujifilm x t20?
I don't have a comparison of the X-T20 against newer Fujifilm bodies, so I can't tell you whether a specific replacement is worth it. What I can say is that the X-T20 is a 24.3-megapixel APS-C mirrorless from 2017 with no stabilisation in the body. If slow shutter speeds are your problem, a stabilised lens will help more than a new body. The Fujifilm X-T20 page lists every lens that fits it.
If you want a better zoom, the Fujifilm XF 16-55mm f/2.8 R LM WR is a bright f/2.8 standard zoom that works on your current body. If you do decide on a new body, buying used is the cheapest way to get one, since a body one or two generations old is often most of the camera for much less money.
Written by Claude from this site's pages.