More important than which camera is which lens; as features are in the camera, while quality is in the lens. A great camera with a poor lens generally won't have the same results as a mediocre camera with a professional-grade lens.
The route to take is find the lens that is the best for you, then find an affordable camera body that can fit your needs.
Like anything else, there are tradeoffs. Something like this will give you a long reach, but the image quality is so-so.
On the other hand, if you want great image quality and long reach, be prepared to shell out one arm, both legs and a couple of toes for something like this. (And be sure to budget a few bucks for the camera to go with it).
Not a lot of information in your question. Since this is a Canon and RF forum I will only include them. Category is General Full Frame.
How much of a distance and how much do you plan to crop? For Canon FF you are looking at 20, 24 and 45 megapixels. If just static subjects the first mirrorless body - the R has 30mp, is a great price these days and has an excellent sensor. With 45 you can crop more but will cost more. Cropping has its limitations as well. If the image is not tack sharp to start with the less you can push cropping. The greater the distance to the subject the more atmospheric distortion you may encounter depending on where you shoot. Also all the bodies have different features which also impacts pricing.
Like others have said the lens is just as if not more important than the body. A basic R with a RF 600 f4 will do much better than a R5/R5II with a 100mm lens even if you can crop more with the R5/R5II. That is an extreme example but these things need to be considered.
R or RP and EF 400mm all second hand you might be lucky and find something, you haven't stated budget or genre.
R5 and rf 100 to 500 good option but $$$ see some good deals on new R5 version oner about the place