I changed my passphrase around march 2018 and now I can't use my new passphrase on the new bitcoin core version. When I put the back up wallet.dat into the new versions of bitcoin core, it tells something about my wallet not being compatible? So where can I download the older versions of bitcoin core, especially version 0.16.0 because it was around that time that I changed my passphrase and back up my wallet.dat. I have tried bitcoin core versions 15.1 and 16.1, but they don't work, so I think 16.0 will work because this was the time with the segwit wallet issue. Or if there is another possible solution, please let me know. Thanks ahead of time.
So, even though I agree with Andrew that you may use other minor versions (e.g. 0.16.1, 0.16.3) without any loss, but when it comes to merely helping you to download your desired version, you've got a couple of choices: