Bitcoin core v0.19.0.1 automatically prunes? Just finished syncing the whole blockchain after days and I realize the bitcoin settings were "pruning", which means I cannot use it as a wallet. 

is it the normal behavior of bitcoin core v0.19.0.1 to automatically prune the blockchain ?
No, the default behavior of bitcoin core v0.19.0.1 is still the non pruning mod.

You should check your bitcoin.conf file depending on your operating system there is a line about pruning which should be something likeprune=550 in your case, just put a # to deactivate it again like #prune=550.