This flickering happens with all shaders I've tested so far aside from AstraLex. Some shaders make it more prominent than others. This happens when only sodium 0.5.1, iris 1.6.7, model fix 1.14, and quilted fabric api 7.1.2 is in the mods folder. I just used Ok Zoomer to zoom into the block corner, which makes the effect more noticeable, but it is still visible with a wide FOV. The shaders used in the clip is Complementary Reimagined, but I have also reproduced the issue with BSL, Solas, and Super Duper Vanilla.

To this core this mod is extremely simple. If you don't consider items all it does is allwoigb tweaking how much of the block surface a texture occupies to 100% of the texture itself. The reason the game does use the very edges of textures is to get around artifacts like these, interns creating others like are visible in some models. For me I didn't experience any but this of course depends on one setup and hardware as rounding errors can play a role too. If you are experiencing visual artefacts you can try tweaking the configs or don't use the mod