>>11854658
Wait, nevermind, I'm retarded and you can do exactly that
If for example you set the aspect ratio to NTSC in Mesen's core settings and in Retroarch's settings you change the integer scale axis to Y + X, you'll get something between NTSC and 4:3, which is IMO pretty acceptable, and you won't have any shimmering and the scaling will be clean, without any shader