You are running 32-bit TModLoader, which has a hard memory ceiling of approximately 4GB regardless of any -Xmx argument you pass. You must switch to 64-bit Java for TModLoader to actually use more RAM.
The 1.5GB wall tmodloader 64-bit breaks
The 32-bit Java virtual machine reserves a fixed 4GB virtual address space. The operating system, Java's own internal structures, and garbage collection overhead carve out large chunks. In practice, the maximum usable heap for modded Terraria under 32-bit TModLoader is around 4GB. This limit applies regardless of what you type in -Xmx. When you try to allocate more, Java simply ignores the excess. It does not error during startup. The game runs until it reaches that ceiling, then throws an OutOfMemoryError. That error often looks like a mod bug or a corrupted world. This is not a Terraria or TModLoader issue; it is a fundamental Java limitation. If you want to allocate more RAM to tmodloader, you must first ensure you are using a 64-bit Java runtime. The 32-bit version will never respect values above that 4GB threshold. If background processes are competing for memory, you can clear RAM on a Chromebook to free up system resources before launching the game.
Checking which Java tmodloader actually uses
Many TModLoader installations bundle their own 32-bit Java runtime inside the game folder. This is especially common with Steam or manual downloads. The bundled runtime ignores whatever you have installed system-wide. To check which version is active, open your TModLoader launch directory. This is usually Steam/steamapps/common/tModLoader. Find the tModLoader.exe launcher. Look for the TModLoader executable inside the installation directory. Right-click that executable, select Properties, and check the Details tab for "64-bit" or "32-bit". Alternatively, run java -version in a command prompt while TModLoader is running to see if the process matches. If it shows "32-Bit" or "Client VM" without "64-Bit", that is your culprit. The fix here is to switch to a 64-bit runtime.
Forcing 64-bit without breaking your mods
To replace the 32-bit version, download the tModLoader64bit.zip file from a trusted source. Then, add tModLoader64bit.exe as a Non-Steam Game through the Add a Game option in the Steam client to launch it. Alternatively, you can extract the contents of tModLoader64bit.zip into the TModLoader installation directory, overwriting existing files. Verify file paths match. Do not change any .config files inside your mods folder. Those are for mod settings, not Java allocation. If you accidentally corrupt your save data, restore from a backup. This process only changes the Java runtime, not your worlds. The same 1.5GB wall applies on any 32-bit OS.
The 32-bit TModLoader runtime cannot address more than about 4GB of heap space due to its inherent architecture, so your allocation is silently ignored and the game crashes with an OutOfMemory error after hitting that invisible wall.
