What should I do about "warning ... unmet peer dependency" when using yarn?

I used yarn to install almost 1000 js libraries. When it's done I run yarn install --check-files and it warns me that it left out just a few. I find this bizarre that it installs almost all and only warns about not installing a small handful (but I'll read up on why yarn's doing that later), for now, I need to figure out what to do about these unmet peer dependencies?

Example output

yarn install --check-files    
yarn install v1.22.19
[1/4] 🔍  Resolving packages...
[2/4] 🚚  Fetching packages...
[3/4] 🔗  Linking dependencies...
warning " > babel-loader@8.3.0" has unmet peer dependency "@babel/core@^7.0.0".
warning " > babel-plugin-polyfill-corejs2@0.3.3" has unmet peer dependency "@babel/core@^7.0.0-0".
warning " > babel-plugin-polyfill-corejs3@0.6.0" has unmet peer dependency "@babel/core@^7.0.0-0".
warning " > babel-plugin-polyfill-regenerator@0.4.1" has unmet peer dependency "@babel/core@^7.0.0-0".
warning " > bootstrap@4.6.2" has unmet peer dependency "popper.js@^1.16.1".
[4/4] 🔨  Building fresh packages...
✨  Done in 1.52s.

My guess is simply install them with

yarn add @popper.js@^1.16.1
yarn add @babel/core@^7.0.0-0

I'm not totally sure though and want to get it right (also not sure if the first @ and ^ should be there).

Note

Although I already mentioned it above and link to it, I reiterate, that this question differs from What does 'has unmet peer dependency' mean when installing a package with yarn? in that it asked about what a peer dependency is, whereas I (and 90 others) would like to know what must be done with yarn to ensure all (peer) dependencies are installed.

How to solve

Copy the name of the unmet peer dependency from the warning message, and add it using yarn like so:

yarn add '<unmet peer dependency>'

don't forget the ' and ' around the dependency, (and keep the @ and ^ symbols if the unmet peer dependency has them).

Example

The error message in the question has

warning " > babel-plugin-polyfill-corejs2@0.3.3" has unmet peer dependency "@babel/core@^7.0.0-0".

so you'd run

yarn add '@babel/core@^7.0.0-0'

to add it.

Repeat this until all the warnings have gone when you run yarn install --check-files and the output just looks something like this (no warnings any more):

yarn install --check-files     
yarn install v1.22.19
[1/4] 🔍  Resolving packages...
[2/4] 🚚  Fetching packages...
[3/4] 🔗  Linking dependencies...
[4/4] 🔨  Building fresh packages...
✨  Done in 1.54s.