Within the entity browser and multistep selection display, it's possible to select more than the cardinality. It would be better to prevent this so that it replaces your selection rather than add to it. So if you have cardinality 1 and select another item, it should replace the selection. If you have cardinality 2 and you select one, it should replace one of the two selected, not add a third.
https://www.drupal.org/files/issues/2020-10-15/weird-overflow.mov →
Add an entity browser with Multistep selection display with cardinality 1 (or 2 or anything other than -1).
Select more than the allowed number of items. Rather than constraining the selection, it allows selecting and inserting more than the allowed amount. The extra items just disappear. If you have cardinality 1, this means you have to do an extra step of removing the selected item within the entity browser before selecting another.
Constrain the selection to the cardinality limit.
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