In my experience, that 100-400 is a solid choice but might feel short for owls in thick woods tho...

• Canon RF 100-400mm f/5.6-8 IS USM: super light and sharp, way better than the kit.
• Canon RF 600mm f/11 IS STM: massive reach for the price, though it needs light. Ive tried many setups over the years and the 100-400 is definitely the most versatile for your budget. You wont regret it.

Just saw this while scrolling... gotta say, be careful jumping into those long zooms without thinking about the light first. To answer your question, that 100-400 might not be the magic fix youre hoping for in dark woods. I started out with a similar crop sensor setup years ago and honestly thought reach was the only thing that mattered for wildlife. Boy was I wrong. I remember hiking three miles in the mud to find a Great Gray Owl, only to have every single photo come out as a blurry mess because my lens was too slow for the evening light. The Canon EOS R7 has so many pixels packed in that it really shows every little flaw and any tiny bit of motion blur. A few things I learned the hard way:

• those slower apertures basically force your ISO into the thousands
• weight is a massive factor if youre actually trekking through brush
• sometimes a shorter, sharper lens with a heavy crop is better than a long soft one I eventually realized that if I couldnt get my shutter speed high enough, the extra reach was basically useless... I moved to a much faster setup and suddenly those owl feathers actually had detail instead of just being grey mush. Just make sure you dont sacrifice too much light just to get a closer view. If youre in thick woods, those dark lenses are gonna feel real limiting real fast, tbh.