If the workflow node where you need the JWT Authorization header can use an OAuth2 credentials item, with Grant Type: Client Credentials, you might be able to use the same adapter/workaround posted here.
The JWT node is meant to support the server-end of a JWT interaction, for when you want to use/require JWT on something calling into an n8n webhook (e.g. to create a pseudo-session). It’s not for the client end of JWT.