I found a client-side (javascript) solution for automatically scrolling to an anchor on page load, which works for OJS 3.1.2. I put this script at the top of the upper panel of Custom Headers Plugin:
<script type="text/javascript" language="javascript">
function moveWindow (){window.location.hash="#your-tag";}
</script>
and this in our theme’s <body> tag (see this post about how to find a theme’s <body> tag):
<body onload="moveWindow()">
Here is another useful javascript for greatly speeding up the anchor-jumping on internal links such as Navigation Menu Added Items in OJS 3.1.2 (put this code in the upper panel of Custom Headers plugin also, but do not edit this code as it only needs the “#” character, not your entire anchor tag):
if (window.location.href.indexOf('#') == 0) {
let hash = window.location.href.split('#')[1];
let hashTop = document.querySelector(`#${hash}`).offsetTop;
window.scrollTop = hashTop;
}
The above three pieces of code handle all of the main requirements of anchor-linking in OJS 3.1.2 (internal anchor-linking, auto-redirect to anchor after subscribing/logging in/registering/searching, as well as archives browsing, etc.). Of course, this is a temporary solution which works if java is enabled in a browser (most browser nowadays by default).
Other issues remain unsolved: breadcrumbs (a shortcut HTML for transplanting breadcrumbs into Static/Custom Pages would be great, something like in WordPress!), and backend styling (colors primarily).