I had it today in Pycharm. Like you, I have been using Pycharm for many weeks without an issue. I suspect a file corruption within my project package manager, possibly caused by an unplanned power-off of my laptop.
To lead with, in a strict dev environment I'm sure you should only create a new project, copy any dependent files/scripts to it and rename rather than delete the corrupt project, if only to preserve the file version history. Then, re-install any non-standard packages as required.
I wasn't, so what I did was as follows. On Windows 10, I clicked on File - Settings - Project: 'yourprojectname' - Python Interpreter. If on MacOS, follow your equivalent path to same.
In the Package window on the right I could see no installed packages and an error message. Out of curiosity, I tried clicking on the '+' button at the top of the window to add libraries back in but got an SDK error. Besides, it already appeared I had a compromised environment package environment so thought it best not to pursue that.
Instead, my solution - and I must emphasise this was on my home laptop for learning purposes only - was to click on the line above that installed package window showing the current interpreter for my project, clicked the down arrow, then 'Show all' and then picked up the interpreter for one of my previous projects in which I had used the same non-standard package. In my case Pandas was the only one.
That fixed it. After that, I could add or delete packages as required. To repeat though, best practice would almost certainly be to create a new project and add your dependent packages and files to it as required.