I think, the latest version of Bitcoin 2 Core (I'm using bitcoin2-2.3.1-win64) have serious bug with importprivkey command.
Firstly, I was unable to import my private keys by using importprivkey command. Right after entering importprivkey command, the Bitcoin 2 Core program executes re-scanning and then shows proper BTC2 address on the debug console. Despite of re-scanning process, BTC2 balance doesn't changed in my wallet (above mentioned BTC2 address have some coins on it). Furthermore, I have executed dumpwallet command and couldn't find either newly-imported private key, or newly-imported public BTC2 address inside of text-dump of my wallet...
Secondly, the importprivkey command doesn't handle properly "rescan" parameter. Regardless of this parameter (false/true), the Bitcoin 2 Core program ALWAYS executes re-scanning process.
What are Your suggestions? - How do I import my private keys?
This got answered on Discord but for the record: Nowadays you can practically speaking only import your BTC2 keys. Not BTC ones like you were trying to.