The library folder is a large cache containing imported assets and other data from the project after import. It is generally always 100% safe to delete the Library folder. As Unity has become more stable, this has become much less necessary than it once was.

Unity provides this tool in C:\Program Files\Unity\Hub\Editor\2020.2.1f1\Editor\Data\Tools which allows you to inspect data in the Library folder.

Contains the serialized, imported data keyed by an asset's GUID. ¹⁾ binary2text.exe can be used to dump and view the cached imported data.