The vscode.previewHtml command has been deprecated since the introduction of the webview API. The webview API is significantly easier to work with, correctly supports different filesystem setups, and webviews also offer many security benefits over htmlPreviews. For these reasons, we would like all extensions to switch over the using the webview API and eventually remove the vscode.previewHtml command entirely.
https://stackoverflow.com/questions/63069694/i-get-the-command-vscode-previewhtml-not-found-error-message-on-vscode