It is apparently possible to revert your PS4 to its previous firmware version, without any backup - Wololo.net
PS4 9.00 Jailbreak. Should you update your PS4 to 9.00? - Wololo.net
PS4 9.00? Buying advice!? help!? | GBAtemp.net - The Independent Video Game Community
PlayStation 4 OFW 9.00 Jailbreak released, can reportedly affect PS5 consoles as well | Page 10 | GBAtemp.net - The Independent Video Game Community
PS4 Update 9.03 is now available, and here what it features and process | by Angelinaolivia | Medium
Don't fall victim to FAKE PS4 9.03 Downgrade Apps - YouTube
According to theflow0 disclosure for BD-JB exploit, here is some table chart which exploit is working and which exploit is not working for each console PS4 and PS5 with their respective firmware :