Updated to 1.8.4.5:
Fixed a bunch of issues with the dark theme.
Fixed focussing in the tree view.
Added Str preview support.
Added support for RSW version 0x206.
Fixed another packed DLL issue regarding GRF encryption.
Extracting resources will now export all files.
Added more checks when saving GRFs beyond 4 GB.
I've added a "fix" for this issue, but like I said last time, it isn't an issue. GRF Editor will now prevent you from saving files past 4 GB of size. If your GRFs are reaching that size, you will need to use another GRF alongside for your client. There are no other solutions.
Should be fixed now.