There are multiple possible reasons for this to happen. One of them - also the one I’d consider most likely - is missing write permissions.
This might be part of the problem. If you’re using the third party launcher, it might tries to save the files at a location with higher protection.
Try downloading the game directly from the website/GitHub and unpack it at a location where this isn’t a problem, start it and see if this fixes it. If it does, consider to change the game directory of the launcher to this location.
You could also try to set the game (not the launcher) to run as an administrator and see if that fixes it.
To help further it would be necessary to know…
- if you’re actually using the third party launcher.
- the game version you’re (trying to) play on.
- your operating system.
Also, for the future, please use punctuations. I’ve now tried to read this sentence for 30 minutes and all I’ve got was a massive headache.