Error that doesn't allow me to play the game although it's my first time downloading the standalone. Asks if the pck file is missing
Generally, people get that error if they try to play the game without extracting all of the files. Unlike simple programs, the Godot executable that runs Strive is rather generic and has almost none of the data and code specific to the game. The executable will try to run the game using the rest of the files and a .pck file is one way of storing those files.
Try to extract all of the files from the archive to a new folder. If the error persists, then download the current version of Winrar or an appropriate archive extracting utility. At some point the format of the archives changed and are not backwards compatible with older utilities.