I couldn't read this without saying please don't despair!
I was the kid who would rather starve than eat something I didn't like. It took me a long time but I eventually got diagnosed with ARFID, I'm not saying that's what this is as toddlers are often fussy monkeys at times but my DM often said she was close to tears as people suggested time after time that she shouldn't offer me anything else.
My diagnosis came late (I was 16) but honestly, I applied the same logic as I would a fussy toddler to get past it. Basically whenever I cooked something, I had a backup of something I knew I liked (for a toddler I'd serve it at the same time).
So for example in your case i'd offer the pasta with a small bowl of cereal on the side (or a slice of bread or something you know is a sure thing he'll eat). Then you're confident he's eaten something without getting into a "I want something else" battle. He will probably eat the cereal, ask for more, at which point you can confidently say "no DS there's no more cereal tonight, you can have some more tomorrow" and leave him to it, he might try the rest of his food, he might leave it. Ignore ignore ignore and never comment on anything he's eaten/not eaten unless he mentions it. Just clear away at the end and rinse and repeat at each meal time. Hopefully you get to the point where he's eating a bit of both and you can reduce the amount of cereal each time.
Honestly the moment someone says to my toddler "why don't you just try a bite" I know it's a surefire way to get her to not even think about trying it.
If you have Instagram there are some good resources to help with this, you're not the only one (kids eat in colour is a good one off the top of my head).
Good luck and just remember for most toddlers this is just a short phase and he'll soon be eating you out of house and home when he's a teenager!