I would say it depends on the formality and time of day of the wedding, and I guess part of the world/country. In my area you would only wear flat open toe to like.. a BBQ. You want sandals (flat) but think you need heels, is that right? Have you considered a formal peep toe? https://www.amazon.com/DREAM-PAIRS-Womens-Dories-Nubuck/dp/B073HB8D5H/
Side cutouts/open side are also very breathable if you live in a hot area: https://www.amazon.com/DREAM-PAIRS-Sole_Vogue-Fashion-Stacked/dp/B078TN3DWG/
Or do both! Peep toe plus d'orsay style: https://www.amazon.com/INC-International-Concepts-Womens-Champagne/dp/B07JYKJ33W/
90s style block heel + bar strap is very in and formal enough for an evening semiformal wedding: https://www.nordstromrack.com/shop/product/1939566
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Now, if you want to wear heels, do it! All my suggestions were based on thinking you wanted low/no heel.
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