There are coins that you can restore your wallet via mnemonic phrase or private key but unfortunately in ada wallet there is no option to restore your coin via private key. Just like what is happening now, many ada holder in atomic wallet cannot exchange or withdraw their coin; atomic wallet has an ada private key but you cannot use it to mainnet.
Is there any plan for cardano to include wallet restoration via private key…
You can raise feature requests (or search for existing ones ) here
But there’s more to it than just private key. Atomic wallet implementation isnt open source and there isnt a definitive way to know what derivations , scheme they use . Importing unencrypted private keys native to implementation is supported (or atleast there are ways) , but that does not mean what others develop will be usable the same way.
Copy that .thank you sir…