This is the guidance I'm looking at: https://www.w3.org/WAI/WCAG21/Understanding/reflow.html
For example, in the image below, the highlighted red container scrolls horizontally, but the rest of the page is responsive.
The w3 guidance says 2-d scrolling should be avoided, but I didn't know if that specifically meant the page itself should not scroll horizontally.
I believe that 1.4.10 Reflow is intended to address webpages where the entire page requires vertical and horizontal scrolling to be readable on mobile devices. If yours only requires horizontal scrolling in one small area, then you should be fine.
This may be helpful:
1.4.10 Reflow (AA)
Intent: Having to scroll in two dimensions to view content on a page makes seeing and reading the content difficult. If a user has to scroll in order to see a full line of text, it becomes very difficult to then follow to the next line.
It's also worth noting a couple of things with a design like this: