If you want to get the best performance out of your Steam Deck, you should update your Steam Deck to SteamOS 3.5.1
You can find out how to do this here:
SteamOS 3.5.1 Update - Developer Mode
Steam button ➝ Settings ➝ System ➝ Developer mode ON
Scroll down on the left side ➝ select the "Developer" tab
"Show advanced update channels" ON
Back to "System" ➝ select Beta under Channel
Activate Beta Participation
To do this, press the Steam button in gaming mode and go to settings.
Then select “System” and make sure that developer mode is enabled.
Then scroll down to the bottom on the left side. You should now see a tab called “Developer”, which you should now select.
Now go to “Show advanced update channels” and make sure it is activated.
Go back to "System" and if "Beta Participation OS Update Channel" is available, change that channel to "Beta" and perform the subsequent update. If this option is not yet available, restart your Steam Deck.
After the update, your deck should be set to the SteamOS 3.5.1 beta version. As always, a beta version can have bugs and the like - but the performance increase is significant.
Have fun playing!