Accompanying Files
Observation Details
The manufacturer filter (direct filter buttons) can only be operated by horizontal scroll on desktop and by dragging movement on a mobile device. As the dragging needs a base precision to stop the movement at the right time to reach the wanted filter button, a single pointer alternative for operation / navigation must be offered.
The viewport of the example screenshot is 375×635px, simulating an Apple iPhone 11 Pro. While this is an old device and more current phones do tend to have increased viewport widths, this test would look even more drastic on the 320px viewport width, the WCAG sets for e.g. 1.4.10 Reflow.
As the manufacturer filter buttons are accessible within the filter options dialog window as well, the issue is rated priority "Minor" and the impact on accessibility conformance is low. However, usability / user experience is affected by this issue, as the user is not aware of those buttons being duplicated from the filter option dialog window.
Remediation Notes
Possible methods to remediate and to ensure access to the buttons:
Adding pagination (single pointer arrow buttons)
Reflow to multiple lines of buttons (also see 1.4.10 Reflow)
Note, that the WCAG, and success criterion 2.5.7 Dragging Movements specifically, do not require presentation / layout parity of different devices, viewports, etc. This means, while functionality and information parity is a must, the layout and presentation can be different.
This allows for another method to remediate, by only displaying the amount of buttons, fitting the available space. So while "all" buttons are shown on larger viewports, the number can decrease on smaller viewports, as long as the functionality parity is met, which is the case, with the filter buttons being accessible via the filter dialog window.
Positive side-effect of the latter option is one less mechanism (horizontally scrolling items) to be maintained.