I agree with the problem statement. Note, that I think that's general usability issue, not an accessibility issue.

I'm of the opinion that there doesn't need to be an icon to indicate an open task, as it's the default state.

Barring an alternative icon that universally conveys "open" I feel similarly, though that may be simply what I am used to since the icons are new.

Agreed that it's not the best icon choice or placement. The markup used in that UI makes it difficult to achieve a consistent result without making more drastic modifications to the code. I'll look into what can be done to improve it without too much surgery.

Proposal: How about the unckecked-box icon for open tasks:

This:
instead of
This:

Hmm. FWIW, I see that and think "I don't have some emoji coded properly"

I am struggling to think of an alternative! Is it possible to have no icon?

I can omit it from the workboard cards, however, now that it's been pointed out, the just doesn't seem right for other places where it represents status.

On task lists and tasks themselves, the icon represents priority (with color) and status, not just status. I think it's important that the default icon there have a fairly large amount of fill so that the color information can be seen easily. I don't see as being problematic in this position, as it's conveying priority as much as it does status. It's also the Phabricator default and what people expect to see there.

On workboard cards, however, task priority is displayed on the left card border, so the icon displays only status. That's the position where it's out of place.

In T297249#7558358, @AntiCompositeNumber wrote:

I'm of the opinion that there doesn't need to be an icon to indicate an open task, as it's the default state.

+1.

in this position, as it's conveying priority as much as it does status […]

This is how I've perceived it as well, the color is what I see it for mainly. The icon is just to have something to apply the color to. On workboards, cards express priority through border color instead. I do note that while this would normally be an accessibility concern, in this case the task header already displays the status in clear text as well: Open, Need Triage for example.

The color is useful as a faster way to recognise statuses when viewing tasks without needing to read. At least me I rarely read the label, I almost always recognise the priority through the color in the header so that's quite useful indeed, so long as it's some kind of fairly-solid icon. A white square with a thin line probably dilutes that a lot, next to removing it entirely. If we recognise it as this purpose, a solid square might work.

Although even then, it seems like it'd be best left out of the already crowded workboard cards. Both the status symbols and task type symbols are imho not adding net-positive value to workboards.

Hmm. FWIW, I see that and think "I don't have some emoji coded properly"

Yeah, I also mistook it for a Tofu character.