Render resolution will always affect memory usage. The question is by how much, because we don't know what kind of resolution the PS6 and the handheld will use.
Let's imagine a game is running at 720p. That is 1280x720x32/8= 3.5MB.
But if a game is running a 1080p. That is 1920x1080x32/8= 7.9MB.
And at 1440p that is 2560x1440p= 14MB.
Modern games will use dozens of rendering buffers, for all sort of things. Though some buffers will use 32bits, other 16bits, and other even 8bits.
So the difference can go to up to 1 or 2 GB of vram.
But still, not enough for the 24 vs 30GB, like you said.