glFramebufferTexture2DMultisampleEXT is available through GL_EXT_multisampled_render_to_texture and EXT_framebuffer_multisample. There's also a relevant Apple extension APPLE_framebuffer_multisample, but GLES on Apple targets is best effort.

One caveat is that Impeller's 2D renderer (Entity layer) relies on the ability to store multisample stencil attachments between RenderPasses, but crucially, the full multisample color attachment is always resolved to a single-sample resolve texture and never stored as a full multisample color texture (although impeller's HAL design does allow for this).
Avoiding multisample color storage is crucial on Android due to the extreme bandwidth requirements.