Cracks on tire - still safe to ride?
The type of tire cracking that is most worrisome is when it's accompanied by bulging areas from the tube pressure. This implies damage to the casing, which in turn implies a tire that might very realistically fail at any time. The casing is the major structural part of the tire, not the rubber.

Cracks in the rubber like this look bad but almost never result in any issues themselves. When they do, usually its actually something along the times of the casing getting damaged in some kind of incident or condition that also caused the rubber cracking.

There's some distant hypothetical risk that the crack makes the casing more vulnerable in that spot or causes some kind of stress riser, but basically it's fine.