Gross motor delays

Britt 🌲
My 10 month old has gross motor delays and has recently begun working with a PT through Early Intervention services. He has only recently started to roll, and doesn't have the core strength to sit up independently. He's not crawling, sitting, or showing interest in doing so.
I've just started exercises where I'm supporting him in a sitting or tummy time position, and he fusses and fights me, wanting to roll onto his back. This is hard. I feel like whenever he plays, I need to be actively forcing him to sit up, which he doesn't want to do. It's harder to get other things done and let him play independently.
Anyone else going through this? Any words of encouragement that you can offer me?