Brand new S20+ ATT branded. Placed in service on Tuesday, 16 June. Checked then and had no updates. Active less than 48 hours. Got two updates Thursday, 18 June -- after second one, I'm now on ATE6 with 1 May, 2020 Security Patch.
Otherwise, I have no idea what additional updates/fixes might have been included. I strongly suspect we will see another soon, as unlocked versions and Verizon versions are now on 1 June Security Patch. Apparently, one of these latest versions includes some auto focus tweaks for the camera system, maybe.