https://tools.infinus.ca/wpDatabase/

{
    "Version": "DB Version",
    "1.2.2": "2540",
    "1.5": "2541",
    "1.5.1": "2541",
    "1.5.1.1": "2541",
    "1.5.1.2": "2541",
    "1.5.1.3": "2541",
    "1.5.2": "2541",
    "2.0": "3441"
...
}

Ideally you'd just call this after getting db_version from your wp_options. Maybe something similar to this?
function dbVersionToWPVersion($dbVersion) {
        $wp_version = ‘Unknown’;
        $url = “https://tools.infinus.ca/wpDatabase/”; // this is json
        $json = file_get_contents($url);
        $data = json_decode($json, true);
        foreach ($data as $wp_version => $db_version) {
            if ($db_version == $dbVersion) {
                return $wp_version;
            }
        }
        return $dbVersion;
    }