Issue When using the Create a new record action (CDS current environment) connector, the Description field is a string field for the Email Message entity. A Power Automate maker cannot apply rich text to the email message through the Description field.
In Dynamics 365 classic workflows this is standard functionality as a Rich Text Editor is provided when using the following steps
Send mail step
Create step when Email is the entity selected
Refer to below screenshot. Action For parity of Dynamics 365 classic workflows the Description field needs to have Rich Text Editor functionality when the entity equals Email Messages for the CDS Create a new record action and CDS Update a record action.
Or a new CDS action is made available that is dedicated to authoring email messages as HTML, similar to the Outlook Send an email (V2) action.
Regardless of the action taken, it would need to be applied to the standard connector and current environment connector for CDS.