Technically it is possible to open a "*.lib" file in the Codesys 2.3 IDE if it is not encrypted, but I know that the IDE is customized according to the vendor. For example, I don't have "native Codesys 2.3" (directly provided by 3S Software) installed on my computer, but a version of SEW Eurodrive (PLC Editor), which contains some modifications dedicated to their PLCs. This version allows me to open *.lib files:

Maybe the version you have doesn't allow this.
Here's a way to test it:
If you create a project, add some function blocks and select "Save As" you will see that there are several options:

If you select one of the "Encrypted" options you will immediately be asked to enter a key, which will be prompted when opening the *.lib file.