He might also be fussy because he’s not drinking much milk there. He is only 8 months but his daytime feeds are mostly purée, due to rejection of milk at daycare.

The sleep train is not a bad idea but that’s up to you to decide. But let’s think about why. You don’t want to hear him cry all night… but you are listening to him cry all day because you suspect it’s due to nap problems. Sounds like you are avoiding one problem without realizing the other problem being created by that avoidance. This is not to say you need to sleep train if you don’t want to, it is to help reframe your thinking. You don’t want your baby to cry at night but you don’t mind that the child is crying at daycare? The daycare workers cannot replicate what you’re doing at home. And they are trying to put him to sleep because overtired babies are also very fussy and hard to deal with. What do you want them to do? Just not try to get your kid to sleep and let him cry all day due to being tired?

He’s having 1) feeding issues with milk and 2) sleeping problems at daycare. Your choice is to do nothing and let them deal with it (=your kid will continue to be angry and fussy every day for a long time) or do everything in your power to get him learn skills to be more successful for daycare. Or you can take him out of this daycare and find another one if you think they’re the problem and not him.