Signtool does not work with MSIX files - can't sign MSIX files with hardware token based key

Question

I am using the MSIX Packaging Tool to create MSIX installer files of a VSTO add-in, based on a ClickOnce-Installer. My problem is that the MSIX Packaging Tool does not allow the signing of the package using a hardware token for code signing, but only .pfx files. When I try to sign the MSIX package using signtool, it tells me that it does not support MSIX. I already tried many workaround with the Sectigo Technical Support, with no luck.

Am I right that it is not possible to sign MSIX installer packages using a hardware based key? Since hardware based keys are the standard, I believe this should be possible. What can I do?

Best,
David