Is there a way to add custom aspect ratios in the image editor?
This will be possible using a new imageEditorRatios config setting that is coming in Craft 3.5 (due to release in early August 2020):
...
'imageEditorRatios' =&gt; [
    'Unconstrained' =&gt; 'none',
    'Original' =&gt; 'original',
    'Square' =&gt; 1,
    '16:9' =&gt; 1.78,
    '10:8' =&gt; 1.25,
    '7:5' =&gt; 1.4,
    '4:3' =&gt; 1.33,
    '5:3' =&gt; 1.67,
    '3:2' =&gt; 1.5,
    'Some custom ratio' =&gt; 1.9,
];

Source (GitHub issue)