When using the flow approval action which uses adaptive cards the formatting options are extremely limited. When using the supported and documented markdowns they work inconsistently across the various methods to consume approvals including
Outlook Online, Outlook Client, Outlook Mobile, Teams Client, Teams Online, Teams Mobile
This results in making it next to impossible to use the few markdowns available as what may look good in Teams online or Outlook online does not work at all in the clients, or mobile, etc. The only option that seems to work consistently is applying no markdowns and just using text which looks unprofessional and provides no structure within the context of the approval. Please either fix the markdowns or provide another solution such as Rich Text when working with flow and adaptive cards.