The best advise is to back up your wallet account and have the seed phrase securely saved somewhere. Make sure not to disclose this seed phrase bc who ever has it can steal your money within minutes. Encrypt your wallet also, just be patient enough to find the best encryption platform.
There are multiple ways in which you can update Bitcoin Core to the latest version. Each one has its own advantages and disadvantages:
Build from source code: You can always update your software by cloning the git repository. This way you can verify the code and build the binary yourself. However, it is a resource intensive task and you will need to ...
Largely, this question boils down to one thing: does the wallet software let you control the private keys for your coins? Or not?
If the wallet does not let you control your own keys (ie a custodial wallet), then it is up to the custodian to craft and publish your transactions. Obviously, this gives the custodian ability to censor your transactions at will.
I suppose it just a succession of lucky event, even if this miner wanted to do a 51% attack, there is not a lot he could have done with it, except as you said break or reduce the trust in the bitcoin network, and someone who have invest that much money into mining equipment must own and will own lots of bitcoin and so have less incentive to try to break it.