Hello there, BigFineMomma!
We appreciate you reaching out here on Apple Support Communities regarding your missing Trash folder in Mail. Let's take a look at it together!
You mentioned rebuilding your mailbox, and whether that would resolve this for you. Typically, rebuilding the mailbox would be used if you're missing messages or the messages might be garbled. You can read more about that at: Rebuild mailboxes on Mail on Mac
That being said, since your iCloud account is an IMAP account, we'd recommend disabling iCloud Mail on your Mac, then restarting the device. It's important to note that when disabling your iCloud Mail, all emails on your device will be removed. However, upon logging back in those emails will show on your device again, as they are safe within iCloud. After restarting your Mac, go ahead and enabled iCloud Mail again. To complete that process, check out: Change your iCloud settings - Apple Support You can also go into Mail > Preferences > Accounts, and deselect "Enable This Account".
Let us know if that resolves it for you.
Cheers!
