Which exact version of Grafana are you using? What HTML have you tried or is not working?
You say you tested the sanitize_html option but I can’t see any such option in v7. Perhaps you are using an old version text panel in the new version, what happens if you create a new text panel in Grafana 7?
For me on a nightly build v7.1.0 I have the choice of Markdown mode or HTML mode. And if I select HTML mode it seems to render (at least basic) HTML as expected.
After a “grafana-cli plugins update-all” and then restart all seems to be working.
There were some plugins in need of update but the text panel wasnt on upgrade list.