But there are a couple of reasons why this is probably not a big problem for MoI.

One is that MoI does not require advanced OpenGL functions, it's not like I've been blocked by anything while waiting for them to update to a new OpenGL release level. It seems likely that they will freeze it at the current level and not just outright remove it, we'll see.

The other is that MoI v4 is well positioned to switch to Metal if necessary because part of the MoI v4 rewrite was to use a graphics library called BGFX which supports multiple rendering back ends. So MoI v4 does not make OpenGL calls itself directly, it makes calls into BGFX and then BGFX handles the OpenGL stuff. On Windows MoI calls into BGFX and BGFX uses Direct3D11 functions. So MoI's own viewport drawing code is well separated now from any specific graphics API.

BGFX also has a Metal rendering back end as well. I haven't tried using it yet because it was officially at WIP level when I started using BGFX and also Metal is only available starting on macOS 10.11 while I wanted to support older OS versions than that for v4. I might wait to try it until I'm comfortable requiring 10.11 as the minimum supported platform which is simplest but there is some possibility I could figure out supporting Metal only on 10.11+ while still supporting OpenGL on older platforms. I haven't dug into that yet. But anyway there is a pretty straightforward path to getting MoI to use Metal.