Hi, and welcome
Firstly remember that milk is still the most important food he can get, and will be for the rest of his first year so if he's not eating loads yet don't worry about. He will take to it at his own pace. Yes it's frustrating when they stop eating things they used to and when they don't eat what or how much you'd like them to eat but it's best just to try and relax and follow their lead.
Is there any chance he is teething ? That can make them go off all sorts of food even stuff that the perviously enjoyed.
Sounds like he might have a bit of a sweet tooth at the moment. Definitely try mixing foods. If he likes apple and pear then add them into some veg (or with other fruits) and see if he will eat those. Then you can always slowly remove the apple / pear from the mix once he is used to it. Apple and pear will mix well with most root veg.
When I was weaning my LO I just froze all my fruit and veg purees seperately then would defrost a couple of different cubes when I wanted to mix stuff, so for example he might have a cube of carrot, apple and butternut squash all mixed up together. I found this easier than making a batch of a mixed puree and if he didn't like something I only had the bowlful to throw out and not a full batch. If he doesn't like soemthing today then leave it and come back to it again in a few days or next week.
If he like yoghurt then try making up your own mixing a nice greek or natural yoghurt with fruit purees and getting him to eat some fruit puree that way.
Even sucking on the rice cake is better than just playing with it. In time I'm sure he'll pick up how to eat it but he'll do so at his own pace. Maybe try him with some other finger foods like toast or some steamed veg sticks or pieces of soft fruits (or steamed harder fruits like apple and pear) and see how he gets on with those. You can always get something like a
fruit nibbler to put the fruit / veg in and let him work away on that (can be a bit messy, but it's a really safe way to give them the food to get on with themselves). Be warned though that fruit juice can really stain clothes badly so a good bib is handy with these (as I found out the hard way
).
If you can avoid the rusks then I would - purely 'cause they are pretty high in sugar - even the low sugar ones.
It's hard I know but just try and relax and I'm sure it'll all fall into place in time. Sounds like you are doing just fine, so just stick with it and as long as you have a happy and healthy baby then there really is no need to worry.