The Apple Silicon developer kits were released to developers 5 years ago, and the Apple Silicon version of FCP was released 4.5 years ago. Despite having 5 years, some plugin developers have not updated their products to Apple Silicon.
Rosetta cannot emulate an app with mixed Intel and Apple Silicon code. The app (including all in-process plugins) must be either Intel or Apple Silicon. Therefore older Intel plugins using the old FxPlug 3.x framework will not work with Apple Silicon FCP, because that would form a mixed-architecture process.
Some plugin manufacturers figured out a makeshift workaround: They told their customers how to force Apple Silicon FCP to run under Rosetta as an Intel process. That was possible since the FCP.app bundle contains both Intel and Apple Silicon versions, and there's a terminal command which will force MacOS to run that as Intel, despite being on an Apple Silicon machine. That enabled their old Intel plugins to work, but it cost significant FCP performance and, often, stability.
Since it was FCP that suffered the consequences of this, those plugin vendors did not pay the support cost for all the problems it created. I don't know if there's an official Apple Support policy for whether forcing FCP to run as an Intel process under Rosetta on Apple Silicon is legitimate or not. IMO it should never be done.
If I were in charge, I would divert every support call and question involving this area back to those plugin vendors.
If your main problem is FCP 11 import is not functioning, first verify whether FCP is running as Intel or Apple Silicon: in Activity Monitor's CPU tab, location FCP and look at the "kind" column. Does that say "Intel" or "Apple?"
Note there is a difference between *installing* Rosetta vs running an app under Rosetta. My guess is you may have followed direction from a plugin vendor about how to run FCP under Rosetta, which then popped up a MacOS "Install Rosetta" dialog, and now there's a problem. The problem was *not* installing Rosetta, it is running the Intel FCP under Rosetta.
If Activity Monitor shows "Intel", just shut down FCP, wait a minute, then launch is normally from the dock. It should start as an Apple Silicon process, and Activity Monitor should indicate that. If it starts as an Intel process, let us know, and we'll investigate further.