Before I try anything on my server, I test it in Web Server for Chrome. This lets you run from your directory on your computer. I use FileZilla to transfer the files to my server. If this is the code you are exporting to HTML5, it works for me using the Web Server for Chrome:
// Project: Hello Test
// Created: 2020-05-25
// show all errors
SetErrorMode(2)
// set window properties
SetWindowTitle( "Hello Test" )
SetWindowSize( 1024, 768, 0 )
SetWindowAllowResize( 1 ) // allow the user to resize the window
// set display properties
SetVirtualResolution( 1024, 768 ) // doesn't have to match the window
SetOrientationAllowed( 1, 1, 1, 1 ) // allow both portrait and landscape on mobile devices
SetSyncRate( 30, 0 ) // 30fps instead of 60 to save battery
SetScissor( 0,0,0,0 ) // use the maximum available screen space, no black borders
UseNewDefaultFonts( 1 ) // since version 2.0.22 we can use nicer default fonts
do
Print( "Hello World" )
Sync()
loop
