To understand the significance, we must look at the numbering scheme. Adobe moved away from perpetual "CS" versions to a monthly SaaS model (Creative Cloud). The year "2021" refers to the feature set released throughout late 2020 and early 2021. is the third minor update to the fourth major update of that cycle.
22.4.3 Release Date: August 2021 Status: Legacy (not the latest, but still useful) Adobe Photoshop 2021 -Version 22.4.3-