Anvil apps generally score a respectable 90 on the SEO dimension in a Lighthouse audit from the onset. You can ramp this up to a full 100 by simply adding meta tags under Native Libraries, e.g.:
<meta name="description" content="App for doing awesome things">
<meta name="author" content="Rufus Anvilson">
<meta name="keywords" content="wicked hipster ubercool">
… whether this actually makes any real difference is another thing… At least it can give you the thrill of scoring a 100 
Rufus