This is what I ended up with:
dim fTemp as FolderItem
#if XojoVersion > 2019.02 then
fTemp = FolderItem.TemporaryFile
if fTemp.Exists then fTemp.Remove()
if not fTemp.Exists then fTemp.CreateFolder()
#else
fTemp = GetTemporaryFolderItem
if fTemp.Exists then fTemp.Delete()
if not fTemp.Exists then fTemp.CreateAsFolder()
#endif
fTemp = fTemp.Child( "myHTMLViewerFile.html" )
if not fTemp.Exists then
dim t as TextOutputStream = TextOutputStream.Create( fTemp )
t.Close
t = nil
end if
while not fTemp.Exists
app.SleepCurrentThread( 10 )
wend
me.LoadPage( strPage, fTemp )