I maintain a list of tunneling solutions[0]. One of the main reasons people choose not to use Cloudflare Tunnel for selfhosting is because technically hosting non-HTML content has been against their ToS. Anyone know if this change affects tunnels?
Therefore, as long as you comply with it (especially the sections 2.2.1 and 2.7), you'd be fine. There are no explicit constraints regarding content type, just on what the content itself is or represents (e.g. illegal stuff).
Disclaimer: I'm definitely not a lawyer.