Create spam filter on missing user before the -at- sign?

Create spam filter on missing user before the -at- sign?

I am getting bombarded with email where the "from" address is always simply @whateverEmail.com
For example:
@aqvwithoutj.top
@azffromx.top

etc. I'm also suspecting the .top domain is going to change.  Any ideas how to create a filter on missing the username before the @ sign?

Thanks!