It's the mount. RF for mirrorless R mount, and EF for cameras with a mirror. If you got the 250D you need the EF one.
For 200 yards I'd say 300mm is the bare minimum you need mate. 400+ would be better but you might want to consider 2nd hand to afford that.
There is a 2nd hand EF 100-400mm L on the Wex website. Pricey, but a lot of lens for the money. Professional level.
USED Canon EF 100-400mm f4.5-5.6 L IS USM Lens | Wex Photo Video