For users looking to download the PS3 system software update or seeking information on the 2021 update, it is important to clarify that these are two distinct versions. Version 4.88 was the major update released in June 2021 , while Version 4.90 was a surprise release on February 28, 2023 .
If you are expecting new themes, menus, or PSN Store overhauls, you will be disappointed. By 2021, the PS3 store was already in a "legacy" state. Here is the literal changelog from Sony Japan: ps3 system software update 490 upd download 2021
Plug the USB into your PS3 and go to > System Update > Update via Storage Media . For users looking to download the PS3 system
Improved overall system stability and performance. or PSN Store overhauls