I’m a little confused about your vet. If she has recommended critcal care, I assume that’s because your boy isn’t eating (enough) on his own? In which case, if he won’t take it willingly, he’ll need force feeding.
If he IS eating plenty on his own, then he won’t need critical care at all.
Force feeding can be incredibly difficult. And I can understand how daunting it is, especially as he’s still so ‘new’ to you. But if it’s needed, it’s needed.
I have had to force feed my doe before a few times. We lured her into her carrier, then put the carrier on top of a high surface (breakfast bar/table), took the top of the carrier off and wrapped a blanket around her ‘burrito style’ I think that would probably be the most difficult bit tbh – the picking and wrapping but if you’re able to do that, syringe feeding is relatively easy. If you don’t know about the bunny burrito, check out youtube for a tutorial. Once bun is securely wrapped, they can’t wriggle or squirm free. You can then lift the upper lip and slot the syringe in the side of their mouth (there’s a gap between front teeth and back teeth – put the syringe there) The most important thing is to push the syringe slowly and stop regularly to ensure bun is able to swallow.
Honestly, I can completely understand your hesitation. It’s scary having to pick up a rabbit when you’re not experienced or confident. I’ve had my boy for 2 years almost and have JUST started picking him up as he needs medication. First few times were stressful but we managed and it’s gotten a lot easier.