I updated my site to WordPress 5.6 last night and afterwards I was unable to increase the quantity of items I wanted to purchase from my store.
I troubleshooted for a few hours and found that is was the theme that was not working with WordPress.
After testing many things I found if I changed the theme to something different the quantity buttons worked.
Things I tried
1) Removed all custom CSS – in case it was effecting it
2) Removed all plugins apart from woo commerce and other plugins needed for the store to actually work – again this didn’t fix the issue.
I had to roll back to wordpress 5.3.3 to get my site working again.