How To Change Phone's "Aspect Ratio" Without PC.
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If your Phone Display Resolution is FHD+
2400 x 1080
This is compatible "Aspect Ratio" for you.
1920 x 1080 - (16:9)
2160 x 1080 - (18:9) or (2:1)
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If your Phone Display Resolution is HD+
1600 x 720
This is compatible "Aspect Ratio" for you.
1280 x 720 - (16:9)
1440 x 720 - (18:9) or (2:1)
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Apps I used
Available in Playstore.
1. Shizuku
2. Pixels: Resolution+ DPI Changer.
Available on F-Droid website.
3. aShell