There are some topics about this question but they are old and I can't believe there isn't a solution for this.
I have made an HTML file and placed it in the Download directory from Android.
When I try to open the file in Chrome, Firefox or Opera I get an error: file:///storage/emulated/0/Download/mysite.html
We are living in 2021 and I can't believe this isn't possible.
Maybe Tasker can help?