Regarding what #1 said, they are spot on. I've used the Canon RF 50mm f/1.8 STM for years and the glass quality for the price is insane. On your R50, that crop factor makes it a perfect 80mm equivalent, which is basically the holy grail for pet portraits.

• Low light performance is solid
• Focus is snappy enough for dogs
• Its basically pocket sized If you find the 50mm a bit tight later, keep an eye out for the Canon RF 16mm f/2.8 STM for wider shots.

Adding my two cents here, i was super stressed about buying the wrong glass when i started. Everyone talks about the Canon RF 50mm f/1.8 STM being the gold standard for budget setups, and honestly, they arent wrong. I bought one used to save some cash and it honestly feels pretty sturdy for what it costs. Just keep in mind that since you have a crop sensor on the R50, you might have to step back a bit more than you expect when shooting inside. If you do go for the Canon RF 85mm f/2 Macro IS STM, just know it is gonna feel way heavier and might blow your budget a bit, tho the compression for pet portraits is really nice. Just stick to the 50mm for now and see if you actually need more reach.

Honestly, grab the Canon RF 50mm f/1.8 STM first. It is pretty much a no-brainer for the price and fits both your cameras perfectly. On the R8 full-frame, it works as a classic portrait length, but on the R50, it acts more like an 80mm lens because of the crop factor. That actually makes it awesome for headshots of your dog since you get that compression without needing to stand a mile away. Sure, a dedicated 85mm would be nice, but finding a decent one under 300 bucks is tough unless you go used. The 50mm is super compact and sharp enough for IG stuff. I have used it for years and it rarely leaves my bag tbh. Just start there and see if you feel like you need more reach later on.