Returnal is quite hard and lacks a proper saving system that amplifies its difficulty curve, but it is actually possible to use cheat codes in the game.
As shared by a user on reddit, there is actually a debug menu that can be accessed in Returnal. Once you are able to access this debug menu, you can use commands with a keyboard plugged into the PS5 to utilize cheats like the ability to respawn and drop weapons.
The first and most important step to follow here is to use a keyboard, You need to find a Bluetooth keyboard that can be connected to the PS5.
You can use various commands on the keyboard to gain access to the debug menu and perform these cheats.
Press and hold Shift, Control, Alt, and then press 1 to 0 to drop different weapons from the game at current weapon proficiency
Press and hold Shift, Control, and then press 4 to respawn at the ship with current health, money, keys, artefacts, adrenaline level, and weapon proficiency. You can also buy another set of weapon proficiency, health upgrade, and artefacts at the shop area once you respawn.
It is important to mention that you should press 3 or 7 when doing these commands. The rest of the numeric keys don’t really do anything special.
If you use these two commands, you should be able to create a build for your run that should satisfy your needs and help you go through the boss fights.
Keep in mind that this can be easily disabled with a future update, but as of update 1.003, this works fine.