Mike's suggestion of the EF-S 55-250mm lens is a good one.
For a little more money Canon EF 70-300mm IS USM (either the original or the II version) also would be good. https://www.usa.canon.com/shop/p/refurbished-ef-70-300mm-f-4-5-6-is-ii-usm
Or, for considerably more money Canon EF 100-400mm L IS USM (either version) would be great for wildlife. https://www.usa.canon.com/shop/p/refurbished-ef-100-400mm-f4-5-5-6l-is-ii-usm But as rather large, heavy lenses (approx. 3.25 to 3.5 lb.) will feel pretty awkward on a small camera like an M50. Both the 55-250mm and 70-300s are quite a bit smaller and lighter, so would be a lot more comfortable on an M50.
I use an EF 100-400mm II, but only on 7D Mark II and 5D Mark II DSLRs fitted with battery grips that make them a lot bigger. Each camera w/grip and 2 batteries weigh 2 lb., which makes them balance much better with that 3.5 lb. lens (and other, even heavier lenses).
I also use a Canon M5, very similar in size and weight to your M50 II. The largest lens I use on it is an adapted EF 85mm f/1.8 USM. That 85mm weighs about 1 lb. The EF 70-300mm is only about 8 oz. heavier, roughly 1.5 lb. I'm sure the 55-250mm is about the same or less. So those lenses should be reasonably comfortable to use on your camera.
With any of those recommended EF/EF-S mount zooms, you will need an EF to EF-M adapter. Canon makes a good one. https://www.usa.canon.com/shop/p/mount-adapter-ef-eos-m?color=Black&type=New I'm using a "Commlite" branded one that cost $130 less and works fine. I've used a Viltrox and that worked well, too. (I'm still using some of Viltrox macro extension tubes with my M5.) Of course, the adapter will add a little to the length of the lens, as well as a few ounces to its weight.
Finally, when shopping you will probably come across EF 75-300mm lenses. While they are the most affordable telephoto zooms Canon makes, I recommend avoiding them. Some versions lack Image Stabilization. Others use slow, noisy micro motor focus drive. Some come up short in both respects. None of them produce very good image quality... especially out at the 300mm end of the zoom. The only thing the 75-300s have going for them is that they are cheap... very cheap. Any of the above recommended lenses will out-perform the 75-300s in many ways and in my opinion are well worth the extra cost.
Actually the prices for the 70-300 or 55-250mm will be pretty close to or maybe even less than you were budgeting for the RF lens you were considering (but won't be adaptable to your camera). Even bought used, the EF 100-400mm lenses would be more expensive than that RF lens, might be more than you wanted to spend (in addition to not balancing well with the camera).
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2), EOS M5, some other cameras, various lenses & accessories
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