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Try turning off Explorer Replacement (Preferences / Launching Opus / Explorer Replacement) and see if you can then open File Explorer or the Recycle Bin (which should open in File Explorer).
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You might also want to try reinstalling Opus over the top of itself, to repair any damaged DLL registrations which might affect things. (No need to uninstall first, and doing so would reset your Opus config, so don't do that unless you want that.)
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If it still doesn't work, try repairing the registry using this:
If any of those solves the problem, you should be able to re-enable Explorer Replacement to get it back again, and everything should continue working.
If none of them solve the problem, you may need to ask for help from the Files App authors as it would appear something was messed up by it if you can't even launch File Explorer now.