Good Evening adamfromma,
We see that you're having a problem with being unable to delete emails on your Mac, and we understand how this can be inconvenient and confusing. We'd be glad to see how we can help with this.
Are you seeing that this happens with a restart of your Mac continuously or does this clear up for a little bit?
If you delete the email by logging into your email account online, not using the Mail app does the email remove from your inbox on the Mac as well?
Also, do you see if disconnecting your internet connection then connecting it again causes this to clear up?
We'd recommend using the Connection Doctor to see if this provides any information on what may be occurring with Mail. For assistance with this, take a look at the following resource:
Use Connection Doctor in Mail on Mac
We look forward to hearing from you.
Have a great night.