This block code will make your main content of blog reverse the order with the right sidebar (Jekyll, Bootstrap 4.5, Responsive)

reverse_order_content_and_sidebar.html

<div class="container-fluid">
	<div id="blog_wrapper">
		<div class="row">
			<div class="col-12 col-lg-9 order-lg-first order-md-last order-sm-last order-last">
				{{ content }}
			</div>
			<div class="col-12 col-lg-3 order-lg-last order-md-first order-sm-first order-first">
				{%- include right_sidebar.html -%}
			</div>
		</div>
	</div>
</div>