On the world map there is a bit of flickering of the images as you move the mouse around. I think it is due to the scaling settings and how partial pixels are being calculated as things move. The horizontal lines in the background also seem to have a bit of this, though the colors blend, so it is not as noticeable. Alone the background might be fine, but the other images accentuate it. For pixel art the Stretch Mode of "canvas_items" is usually a good choice, and might help with this.
Looking at the web console, I see that you are using a shader that is getting an error, so maybe that is also affecting the display. Below is the console output of the 4 errors shown, all on the same line.
index.js:485
SHADER ERROR: Built-in function "fwidthFine(vec2)" is only supported on high-end platforms.
at: (null) (:13)
ERROR: Shader compilation failed.
at: set_code (drivers/gles3/storage/material_storage.cpp:2631)
If you primarily run/test this on desktop instead of in browser, you may want to try testing with the Compatibility Renderer. Web is exported with it, and it does have some limits for shaders.
The tutorial mentioned things at the side that I did not see. With the console open I found that that there was more to the UI that had been cut off. Even then it was still cut off, but I could see there was more. You may want to look at your scaling to see that you have it set to keep the aspect ratio.
Note: I am playing in a web browser (Vivaldi, Chromium based), and on Linux. I normally keep my tabs in a panel on the left side, which does make the page area less wide than 16:9. Generally games are able to scale to fit, with empty space above and below, for 16:9 resolutions. I am also playing on a 4K monitor with the browser not at full screen. I was able to resize my browser window to show the full game. I also have a 1080p side monitor, and, with the left panel closed, the game displayed fine.
I see that you have a link to Steam, so you may not want to spend as much time on web compatibility, but if you are planning to keep a web preview, you may want to improve it to better scale on multiple browser window sizes.
I found the text hard to read, primarily white/light colored text. Again, not knowing what your shader does, maybe it would help. I tested on both monitors. The 1080p looked worse, as the 4K does some smoothing. I don't recall the name for it, but the edges of the white text had that RGB artifacting effect where you see more of one color than the others. Combined with the horizontal lines of the background, I think they combined to make things harder to read. This stood out more with the tutorial text coming up while the enemies are on screen moving and you need to read and react.
While playing I had several lags. The most notable were after I had let it sit for a while as I was writing some notes, but even after restarting I had notable lags causing me to jump around and miss shots.
I think the core gameplay works well for a match 3 shooter game. The marbles having special abilities, along with items offering bonuses is nice. Being able to pick up more of them as you progress adds some variety and replayability.
I don't play this style of game that often, and spent a lot of time testing and reviewing the initial issues before getting to playing, plus the lag issues, so did not end up playing for that long. I beat the first level once, and had too much lag on the second, so restarted. I played a bit, then had some more lag, and that is when I stopped. My partner plays this style more than me, and will play it as well to give better feedback on the gameplay.