Is the BACPAC from a TDE encrypted DB also encrypted?
No, the BACPAC is not encrypted. BACPAC is an export of schema and data.
TDE means that decryption is done when SQL Server reads the data pages from disk. I.e., the client tool that generates the BACPAC (sqlpackage.exe, for example) asks SQL Server to read the data, and that tool will never see the encrypted data.
So you'd have to post-encrypt the BACPAC file by some tool, if you have such a requirement.