I know you're sleep deprived, but at 8 weeks old the baby
should be waking for night feeds

They have such small tummies, and the milk is digested so quickly, that they need to feed again in a few hours. You can't expect your LO to go through the night on one or no feeds. My LO was still waking at 12 weeks, and I would think the majority of babies would even beyond that.
Rusks contain wheat, which shouldn't be given to your baby before 6 months. I'm not sure if there are gluten free rusks available (there aren't any gluten free ones here). An alternative is baby rice, which is safe to give younger babies, but again, solids aren't recommended before 6 months unless there is a medicalo reason for it.
Putting any kind of solid into a bottle is also not recommended. It's something people used to do, but now most HVs etc recommend you don't do it. You get the occasional one that does, but I'm not sure they're following the guidelines if they do. You may also find that the people that tell you to do it became mothers 20+ years ago, or they are new mothers that have been told by their paretns that it's a good thing to do, but they don't necessarily keep up with the medical research.
And research has found that feeding solids before bedtime doesn't actually improve night sleeping. Some mothers will disagree, and yes, your baby may sleep better, but research found it's not because of the solids.