Firstly, welcome.

You could choose a 4/4 Style that has triplets as a feel, but you wouldn't normally be able to enter chords as triplets in the chord entry chart.

If you select the Style Picker, press Clear, select 4/4 Styles from the Time Signature button, and enter the text 'Triplet' in the Filter String, you will be presented with styles that match those settings.

You can enter notation to have a triplet form, but I think that is separate to your question, as it doesn't relate to the chord chart.

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