Thanks people ! I managed to see my funds again, but it was not very intuitive.
I had my MetaMask linked to the Trezor device, so luckily connecting my Trezor kinda fixed things.
I say "kinda" because once I connected my Trezor, it only showed me my ETH balance, all the other Altcoins I had
in all the other Networks were missing. So it was up to me to remember exactly what coins I had and in what Networks.
Fortunately I could do that but it was tedious as I had to re add them to MetaMask one by one, not at all intuitive.
What caused this problem was Chrome accidentally clearing my history ( I must have clicked the wrong button or somethn )
so MetaMask did not recognize I was a long time user and treated me as though I was using Meta Mask for the first time.
I was disappointed it took me a long time to restore my old settings and looking to get rid of my Meta Mask as soon as possible.
I still have no idea what this "private key" is about or the damn .JSON file , that sounds way too elaborate and overly complicated,
I'm not really interested ! I already had a super complicated password, a 12 word seedphrase, and a Trezor hardware device setup,
why ask for more ? To make things worse, MetaMask does not have customer support, when you click on their "contact support" they
force you to go elsewhere and find the answer to your question there, and only come back when you exhausted all other options.
So basically, " get lost, we're too busy for you, just find your answer in the nerds forum and come back next week ".
Not impressed !