The polygon shredder redux, Cheron particles likely are rendering to 32-bit floats or filtering float textures.
Rendering to 32-bit float texture is currently not supported on any iOS device.
Texture filtering of 32-bit float textures is currently not supported on any iOS device.
On 15.3, EXT_float_blend and EXT_color_buffer_float were incorrectly advertised. This bug was fixed in 15.4.
The application should use https://www.khronos.org/registry/webgl/extensions/EXT_color_buffer_half_float/ for both, and work with half-floats on if the 32-bit float extensions are not available.
For hevc video missing transparency, please file a feedback request against Safari at https://developer.apple.com/bug-reporting/ with preferably minimal reproduction testcase. You can also post a link to the reproduction case here