I don't have this issue when making spaghetti, but I do have this issue when making a box of mac and cheese for my kid. I use way less water for the latter, but it's the amount of water they specify on the box.

The way I do it, the boil for both is usually not a rolling boil; the water has just started to bubble and steam. I started doing it this way years ago when someone told me that noodles typically cook (the starches gelatinize, I think) at a temperature just below boiling, so you don't actually need a full rolling boil to fully cook pasta.

I salt the pasta water for spaghetti, but not for the mac and cheese.

If I don't stir the mac and cheese regularly, it will aggressively stick together. The spaghetti will eventually stick together, but takes waaay longer. This never happens in practice because I manually stir every few minutes while I'm making the sauce.