Duplicating HDMI0 on HDMI1 at different resolutions (I.e mirroring)

[StonedEdge]

I'm having a bit of an issue trying to force 2 different resolutions on my CM4 (not even sure if this is possible or not) - thought someone may have successfully figured this out by now/updated the drivers to be able to do so.

I have my internal screen connected to HDMI0 and an external screen connected to HDMI1. My config txt is below (hopefully this explains what I'm trying to do). Essentially I want to force two different resolutions without one overwriting the other. I want the 800 x 480 screen to display at that resolution on HDMI 0, and I want the TV to display 1920 x 1080 on HDMI1.

hdmi_force_hotplug:1=1
hdmi_force_hotplug:0=1
hdmi_group:0=2
hdmi_mode:0=87
hdmi_cvt:0=800 480 60 6 0 0 0
hdmi_group:1=2
hdmi_mode:1=82
hdmi_drive=2
config_hdmi_boost=4

[pi4]
# Enable DRM VC4 V3D driver on top of the dispmanx display stack
dtoverlay=vc4-fkms-v3d
max_framebuffers=2

[all]
#dtoverlay=vc4-fkms-v3d
overscan_scale=1

What's happening is essentially HDMI1 is being overwritten by HDMI0 settings (only showing 800x480) and then screen blanking. Removing the hotplug from HDMI0 seems to resolve the issue - is it not possible to force two different hotplugs/have two separate framebuffers with the fkms driver backend?

As far as I've researched, the drivers still don't allow this to be a possibility, which is quite strange to me as it does seem like a simple thing to be able to implement.

See below image for current issue. This is on the Pixel Desktop, however RetroPie does not load any image on HDMI1 at all (i.e emulationstation does not load) but shows up on HDMI0. When I open pixel desktop, I get a reflected image of what is on HDMI1.
https://imgur.com/a/8TArzYD

It's a bit of a disappointment that the drivers don't support the dual HDMI out, as I was hoping to have a hotpluggable switch-like handheld. Of course I can probably overcome this in software, but doesn't look like it's going to work on RetroPie.