Hi @cyy,
This error seems to pop up when someone's qiime 2 environment is inconsistent or corrupted - maybe you've accidentally changed the R version in it, or something else in the computing environment is interfering with QIIME 2.
It's probably easiest to remove the environment and install a new version (which, incidentally, will get you some nice new features). If that's not an option, it may be possible to troubleshoot the environment, but I suspect that will be more trouble than it's worth. Here's another relevant post, with some of the commands mentioned above (removing an environment, updating conda, looking at everything installed in your current environment, etc).
Good luck!
Chris 