Redactor works great with Grammarly if the appropriate setting is enabled. But if you use data-blocks such as layouts, columns and others in your content. You should set the dataBlock setting, which will change the attribute name, because Grammarly conflicts with the default name in the editor for some reason.
<!-- element -->
<textarea id="entry">
...
<div r-data-block="layout">
<div r-data-block="column" style="flex-basis: 50%;">...</div>
<div r-data-block="column" style="flex-basis: 50%;">...</div>
</div>
...
</textarea>
<!-- call -->
<script>
let app = Redactor('#entry', {
grammarly: true,
dataBlock: 'r-data-block'
});
</script>