1) Did you try changing the columns-per-row to 0 (fluid)? If that doesn't do what you want, v3.6.3 adds a 'soft' configuration setting:
Code:
    // -----
    // Starting with v3.6.3, a categories' fluid layout can be identified.  If predefined (like
    // in an /extra_datafiles .php module), that override is used.
    //
    if ($category_row_layout_style === 'fluid') {
        $grid_cards_classes = 'row-cols-1 row-cols-md-2 row-cols-lg-2 row-cols-xl-3';
        if (!isset($grid_category_classes_matrix)) {
            // this array is intentionally in reverse order, with largest index first
            $grid_category_classes_matrix = [
                '12' => 'row-cols-1 row-cols-sm-2 row-cols-md-3 row-cols-lg-4 row-cols-xl-6',
                '10' => 'row-cols-1 row-cols-md-2 row-cols-lg-4 row-cols-xl-5',
                '9' => 'row-cols-1 row-cols-md-3 row-cols-lg-4 row-cols-xl-5',
                '8' => 'row-cols-1 row-cols-md-2 row-cols-lg-3 row-cols-xl-4',
                '6' => 'row-cols-1 row-cols-md-2 row-cols-lg-2 row-cols-xl-3',
            ];
        }
2) There's a 'soft' setting (see dist.site-specific-bootstrap-settings.php) that totally disabled the back-to-top button. If you still want it to show, but not overlay "important" buttons, here's what I added to my /css/site_specific_styles.php so it overlays the footer:
Code:
#back-to-top {
    bottom: 2.5vh;
}