It's important to note initially that, thanks to the many Minecraft Java vs Bedrock differences, this only applies to the Java edition of the game. You can't allocate more RAM in Bedrock.

You can try the following methods to resolve the Minecraft memory error: allocate more RAM or memory to Minecraft by starting the game using the “Java edition or Options” or “Minecraft ...

How to install and run shaders in Minecraft Enhance your visuals and fine-tune shaders in Minecraft Java Edition.

Run Minecraft Java on your Steam Deck with my straightforward step-by-step guide, using Prism Launcher to keep things simple.