You can send from Hide My Email addresses:

https://support.apple.com/guide/icloud/use-hide-my-email-in-...

I think I've also seen this in Mail.app but that's not shown on this page.

Wow my bad I wasnt aware its possible. I remember someone in HN comments complaining about it being one way only back in 2024.

UPD: apperently this supposedly only work if someone message you first. So you still cant spam from aliases.