Mac OS 10.13.6 with homebrew installed, today had to upgrade it because of new homebrew policy

Can't update or upgrade Homebrew

after doing this, tried upgrading node to latest version and got below error

Warning: You are using macOS 10.13.
We (and Apple) do not provide support for this old version.
You will encounter build failures with some formulae.
Please create pull requests instead of asking for help on Homebrew's GitHub,
Twitter or any other official channels. You are responsible for resolving
any issues you experience while you are running this
old version.

Error: node not installed

In fact I do have old version of node installed

node -v
v12.0.0

how to solve this weird problem ?

Note:

Few weeks back I did below to use older version of node

Install NVM On Mac With Brew

I'm really confused atm, who is managing node on MAC ? Is it NVM / homebrew ?