Advice on leaving puppy alone

Hi all, I have a 4 month old cavoodle who has some pretty bad separation anxiety.

I haven’t gone to my regular sports (usually 3/4 times per week in the evenings) since I’ve gotten him a month ago,

He can handle being in his crate if I am in the room, but if I leave he starts crying.

I sometimes leave him outside for 20-30 minutes, but he will usually just whine / cry or sit by the door. He won’t eat any food or treats if I try leave this out for him in this time.

I want to get back into training (usually will be gone for 2-3 hours), but is this something I will have to put on pause until I am able to address and manage his separation anxiety?

Any advice is appreciated