I don't think so, because the drive can't be unencrypted by the Mac before an OS is loaded.
If you want to encrypt your data, then using FileVault is the best way, and your Mac knows how to boot from a FileVault drive.
However, it will boot to Recovery first, then ask you for the drive's password, then let you boot up.
You probably used an old macOS installer app to create your USB bootable disk.
A lot of macOS installer apps downloaded before Oct 2019/Nov 2019 contain an outdated certification chain and thus are invalid.
Simply download a new OS X El Capitan install.dmg (with a valid cert chain this time), open the dmg and open the InstallOS.pkg. The installer package ...