After upgrade using prepareUpgrade() with Gnosis Safe MyContract.address returns the imp. address

Support Upgrades
2

From the code lines you’ve posted, would existingContract.address, give you the proxy? Or is that your old implementation address?

In my upgrade script, from the tutorial I followed in OpenZeppelin Upgrades: Step by Step Tutorial for Hardhat

I have this

async function main() {
    const proxyAddress = '0xC031c8F6C360E18b232F4728b336AA6394668F48';    // CHANGEIT - change this to your PROXY address, not impl, not timelock, PROXY

    const catnipUpdate = await ethers.getContractFactory("Catnip");
    console.log("Preparing upgrade...");
    const catnipUpdateAddress = await upgrades.prepareUpgrade(proxyAddress, catnipUpdate);
    console.log("catnipUpdateAddress at:", catnipUpdateAddress);
}

You may have to deploy with some arguments, but the first address is the proxyAddress, which would be your existingContract.address