Supervisor has been putting off reading my thesis for months

I’m a Master’s student preparing to submit my thesis for an upcoming graduation session. My supervisor already originally suggested postponing submission to the next session, and I followed that plan. After months of fully working on it and sending revised drafts and waiting for feedback, he now says I may need to postpone again—without having read my work—because he’s been too busy.

He has generally been kind, but he has repeatedly delayed providing feedback. I still don’t know whether the thesis is close to submission or whether major revisions will be required, since I’ve been working largely on my own. He has told me he can only discuss the thesis shortly before the upload deadline due to other commitments, which would leave me very little time to act on any substantial feedback.

What is the most professional way to handle this?

I want to be firm but respectful.