Just in case if you like QR Code and want others to share your post’s URL using simple QR code, there are good news for your. I recently came across goQR which will allow you to do just that using their API.
You can visit their API Documentation page for more details but here is the summary.
<img src="https://api.qrserver.com/v1/create-qr-code/?size=100x100&data=<?php the_permalink(); ?>">
All you need to do is to simply copy and paste the line mentioned above on your single.php page and update it. You are all set.
Now, if you want to get bit more creative with your QR Code representation on your site, I would highly recommend you to visit their API Documentation page and find more parameters. Simply play around with them and you should be able to get your QR Code for your posts.