Photography

I’m trying to pick a DSLR-compatible Canon telephoto lens for wildlife photography in low-light conditions (also, I like doing urban candid photography/street photography from distances, so that too). Naturally, this means high ISO and low f-stop. For some reason, all I can find are like f-4; is that normal? Also, what’s with all the “telephoto” lenses that max out at 200mm? Shouldn’t something like 400mm be better? I suppose I don’t want something too bulky, so 400mm is probably pushing it but idk… if you have experience in this, let me know what you think. I can only seem to find a handful of options, and most are for mirrorless cameras which sucks because I don’t want too many camera bodies so getting ANOTHER one for this purpose would really clutter my shelves as I don’t have any mirrorless Canon’s.

Anyways, budget is tight, nothing north of $1000, let me know what you think!

Edit: Posted in wildlife photo community, but it was dead (no posts since like 2 months ago) so figured I'd move it here.