Compared to other browser-based stackers, TETR.IO is rather resource-intensive. Lower-class devices might have trouble playing the game on default settings. But don't worry, there's a lot of tips on this page that may help you!
1. Use TETR.IO Desktop
The shiny desktop client for TETR.IO applies a bunch of the below patches for you, and tends to give better performance. Download it here.
2. Change your graphics settings in the Config
This may seem obvious, but check anyway. The important options in Config are:
3. Zoom in
When you zoom in on your browser, the game has to render less. The interface will become more cramped, but the game itself will render the same, albeit a bit blurrier.
Zooming in (CTRL+SCROLL upward) a few ticks will increase your performance greatly.
4. Close other programs and tabs
Make sure you don't have 4 other games open. TETR.IO should be classified as a full desktop game, not a random browser tab.
5. Check your power savings settings
Many laptops are by default set to battery savings modes, especially when not charging. Check to ensure your PC is set to high performance mode, and not some battery saving mode, to ensure you're not missing out on performance.
6. Make the window smaller
If you make the window smaller, the game has to render less. This will increase your performance greatly.
7. Try a different browser
Chrome (or Chromium-based browsers like Opera) is generally the fastest browser for this sort of content. If you're not using Chrome, try using it.
8. Ensure Chrome/TETR.IO Desktop is using your GPU
If you're on a machine with multiple GPUs (like a laptop with both an Intel integrated GPU and an NVIDIA GPU), ensure your browser/TETR.IO Desktop is using the high-performance dedicated GPU. Instructions for this differ from machine to machine, but generally you want to take a look in either the NVIDIA Control Panel or the AMD Catalyst.
I tried all this!!!
If you've tried all these steps, and still cannot get TETR.IO playable, your PC may not be able to play TETR.IO. If you need extra help, open DXDiag (hit Windows+R, then type "dxdiag") and save all its data to file. Then, contact me with the DxDiag.txt it creates.
Hope this helped you!