Run the following commands in the frontend directory:
rm -rf ./node_modules ./package-lock.json
npm install vite@5.4.16 Newer vite versions break the code.
Then reinit npm
npm i
Now try building again:
npm audit fix
npm run build
It worked for me and the frontend can be build again.
If that didn't work, then read the next document, the Compiling the Frontend part:
https://github.com/ny4qphil/PhantomSDR-Plus/blob/main/INSTALL.md
Then after you done that, try the above commands again. It worked for me.