Not receiving all emails to custom domain address in iCloud+

I recently migrated from Google Workplace to iCloud+ and using my custom domain email addresses. The domain is with Squarespace. Everything seems to be correctly updated as far as I know, however I am not receiving ALL of my emails. I am getting most of them, but I've noticed there are a few things like some newsletters or email subscriptions aren't coming in. Nothing seemingly too important, but it does have me worried about what else I might be missing, especially if it's a billing/banking email I'm not getting.

My junk mail folder is always empty, so they aren't going there. And as far as I know there is no way to check anywhere in iCloud if there is a list of blocked emails i can approve or something? I am assuming they are just bouncing back to the sender as undeliverable? I'm not sure how I would go about testing this or figuring it out. I tried contacting Apple support but they were unable to help in any way.