When Google created the system around 2011 chromeOS was mainly a mix of features, borrowed from their Chrome browser, where the user experience was criticised for being too web centric.
When early adopters accessed the system they were limited to virtually nothing other than viewing favourite web pages.
However over the years the product has matured and grown into a powerful, and more secure, operating system for handling all kinds of computing tasks.
A key goal for Google was to include the capability for chromeOS to support the running of Android executables. These come in the form of downloadable APKs that are obtained from the Google Play Store or, with caution, elsewhere. Note that another operating system called Cloudready was developed by Neverware to run on non-chromebook equipment. This was purchased by Google and is now available as chromeOS Flex as a fully supported chromeOS environment with the exception that it does not support the running of Android executables.
These products themselves were major accomplishments and were followed by other projects [such as Crostini] to provide a Linux run time environment within chromeOS / Flex adding to the overall capability and appeal to users and developers who now had a much wider and powerful system available to them.
More recently Google added the capability to run native Windows' executables under chromeOS but initially this feature is only available to corporate users and requires the use of more powerful, top-end, Chromebooks - at least for now !
Moving on a decade to early 2021 Google announced LaCrOS that is a Linux version of their Chrome browser. It has been under a lot of development to allow Google to split the tightly integrated Chrome Browser and chromeOS into separate products so that they can be managed and released independently of each other.
This flexible environment makes it possible to host multiple sessions, for multiple users, and switch between them rapidly.
There is extra flexibility and security within the control of a single Desktop environment when two or more user accounts are actively signed in. All of the respective assets, permissions etc. are kept completely separate and private from one another.
At the time of writing the Lacros browser can be run in parallel with the Chrome browser or users can opt to configure it as a complete replacement running in a Linux Virtual Machine.
Press reports have suggested that eventually [as far chromeOS in concerned] Google could replace the Chrome browser with Lacros, but perhaps retain the original name. Either way it should provide a smooth, and perhaps transparent, migration as far as end users are concerned.