Linux is nice for an air-gapped system. Linux is nice for a system connected to the internet.
But let’s not start thinking that we can actually secure an internet-connected Linux-based operating system. It is just not going to happen–that is, absolute security is not possible.
That said, we can play the losing game a little and give our internet-connected OS some attention. It is like you own a house. You can protect it from rats. But don’t think you can protect it from STASI 4.0 or a pimply-faced genius in Novosibirsk.
What you can protect is a device that never touches the internet.
If you think all Linux-based operating systems are utterly or even mostly secure because they are Linux-based, that is mistaken. Linux-based systems might be more secure overall, compared to Windows, but they can still be attacked and subverted.
As soon as your Linux-based system touches the internet, it is no longer safe. This is the unpleasant truth of the matter. However, knowing the truth is a good starting point for setting up a system that offers real benefit (near-absolute security).