When updating:
nodejs-lts-gallium and nodejs-lts-fermium are in conflict (nodejs). Remove nodejs-lts-fermium? [y/n] n
error: unresolvable package conflict detected
error: Failed to prepare transaction (conflicting dependencies)
:: nodejs-lts-gallium and nodejs-lts-fermium are in conflict
It’s OK to remove nodejs-lts-fermium and change it for nodejs-lts-gallium?
It depends what requires those packages. nodejs-lts-fermium (Node.js 14 LTS) and nodejs-lts-gallium (Node.js 16 LTS) both provide nodejs. Certain programs require specific Node.js versions and will not work with older or newer versions.
I will try to remove nodejs-lts-fermium and see whats happen, but I will use pacman.
but there is others implications in this
removing nodejs-lts-fermium breaks the “nodejs-lts-fermium” dependency needed by npm6
npm6 is necessary to apm and apm is a dependency of atom
What I decided: remove atom, as I dont use it. 
how did u remove nodejs ,i m unable to remove it by pacman
The error message suggests that both packages have conflicting dependencies, which means that they cannot be installed or updated together.
If you choose to remove nodejs-lts-fermium and install nodejs-lts-gallium instead, make sure to check that any applications or services that depend on nodejs-lts-fermium will continue to function correctly with nodejs-lts-gallium. You may need to update your code or configuration to work with the new version of Node.js.
What’s the error message?
This is a question from 2022 and I have “nodejs-lts.fermium” installed, i can’t remember what I did and what was the problem. Anyway I think it is solved.
Oh sorry, however, you don’t need to remove any package manually, it will be replaced when you install the other other package:
pamac install nodejs-lts-hydron
(This will remove the gallium version and replace it with hydron.)