Hi @Anonymous,
This is not really a Power BI question and indeed probably better directed to a forum that has a much better breadth of knowledge for OS adminsitration and web development (such as Stack Overflow), but I'll provide what knowledge I can, and this might give you somewhere to go from here.
I can only speak for Windows but .html files are associated with a default browser at the OS level. To make these files open in Chrome you will need to ensure that every single user has their default browser set to Chrome and they will not change it... or ignore the default and choose to open it in another browser they have loaded (which would be possible).
Only having to support a single browser is a luxury that few are afforded - I've never been in a position to do this and can't honestly think of any colleagues I've worked with that have either.
If you can't guarantee the OS/browser your users are going to be using for your content, the reality here is that you'll need to design and test your content to support modern browsers that your users are likely to use and advise your user of what these are so that they can act accordingly. If you only want to support Chrome, advise them to view it in Chrome rather than anything else.
If you're feeling extreme, you could probably write some JavaScript that blocks content based on user agent, but it's not 100% reliable, mostly due to their ever-changing nature and how easy it is for anyone who feels so inclined to spoof things.
For your provided HTML code, this should work in pretty much any modern browser, particularly if you're embedding Power BI content (as MS will handle this part for you), so you'd only need to worry about whatever else you're surrounding it with. The only snag might be that you are specifying explicit width and height for the iframe, which may not be inclusive if a user's monitor is narrower (or not as tall) as this. There's not an easy solution for this, but you could have a look at a responsive solution like this one.
Regards,
Daniel
