You can donate to Qubes OS instead:
I’ve checked a little and it seems that the gui-videoram-min and gui-videoram-overhead features only work for qubes with Qubes OS GUI agent installed. It’s not changing the assigned video ram in Xen config but the dom0 is passing the VRAM configuration using QubesDB.
If you change the gui-videoram-min or gui-videoram-overhead features and start a qube with Qubes OS GUI agent installed then you can check that the VRAM configuration was passed to it:
qubesdb-read /qubes-gui-videoram-overhead
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