I have the @^3.3.0 and @^4.8.2 versions of @openzeppelin contracts in my code for testing purposes. I installed @^4.8.2 with the following command:
npm i @openzeppelin-latest/contracts@npm:@openzeppelin/contracts
The problem was that this file contracts/proxy/UpgradeableProxy.sol does not exist in the latest version.
@openzeppelin-latest/contractslooks odd.
I agree; it looks odd, but it's only used for testing with different versions.