Do multiple UIAbility components run in one or more processes? Can a third-party application run in multiple processes? Will the running of child processes be affected when the main process ends?

PCs/2-in-1 devices

UIAbility components of different modules can run in different processes.
Processes are independent from each other. A process is not affected when another process exits.

Other devices

Multiple UIAbility components run in the same process.
The UIAbility of third-party applications does not support multi-process operation, whereas the ExtensionAbility runs in a separate process.
The UIAbility components of an application designed for a mobile phone run in the same process and do not have child processes.

Reference

Process Model