Sitecore Horizon v9.3 is fairly new, and I could not see any documentation if Horizon v9.3 supports SXA.
Does Horizon v9.3 support SXA?
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Horizon has limited support for SXA. In Horizon, you can open Web pages designed with SXA and edit text fields. You can also add some renderings to a page, but you must create the associated content items in the Content Editor. You cannot add composite renderings like carousels and tabs to the page. You cannot edit rendering properties in Horizon.