TurboWarp blocks
TurboWarp has a section of blocks that allows you to use certain features previously not accessible to Scratch projects.
These blocks will not work in Scratch and projects containing them should not be uploaded to the Scratch website (per Scratch Terms of Use Section 4.4). The only exception to this is "is compiled?", which will work perfectly fine in Scratch (it's not actually a hacked or modded block; you can obtain it using an unmodified Scratch editor)
If you don't use any TurboWarp-exclusive blocks, then there should be no issue with making your project in TurboWarp and uploading it to Scratch. (it will just look like a project made with the offline editor)
This block is pretty simple, it tells you the last block that was pressed. It's intended to be used something like this:
It's like "mouse down?" but lets you check each individual button. Keep in mind that due to how Scratch interprets mouse input, it's possible for a block like "is left mouse button down?" to report true while the standard "mouse down?" reports false.