I just want to know if I can still use this?

Yes, so long as it's not removed from npm registry. You can always fork it so you've a copy. Deprecation just means it is no longer being actively maintained.

You may want to move to tsParticles and specifically react-tsparticles though, as that react-particles-js repo suggests.

Deprecated packages can still be used, and npm generally will never remove a released version of a package unless it contains a security vulnerability. However, the package being deprecated means the developer will not be updating it, and they strongly recommend using another package.