DeprecationWarning: Compilation.assets will be frozen in future, all modifications are deprecated

Update 2021, Feb 25

Html-webpack-plugin v5 is released, just run

npm i -D html-webpack-plugin@latest

or

npm uninstall html-webpack-plugin

npm i -D html-webpack-plugin

Original answer

This is mostly related to html-webpack-plugin, and while its new version 5 (integrated with webpack v5) is still in beta, you should update it manually:

npm show html-webpack-plugin version 
4.5.1

npm show html-webpack-plugin@next version
5.0.0-beta.5

npm i -D html-webpack-plugin@next