Signal package has Electron (which is built on top of Chromium and NodeJS) + Signal app code and assets. So not surprised that it's bigger than Chromium.
A lot of apps you launch do become child processes of explorer.exe. If explorer crashes they might misbehave or become zombie process in Unix terms. It depends on the app though. e.g. Firefox and Edge don’t but Chrome does.
That’s why I run explorer in multi-process mode. Folder windows cannot crash the shell process.
Would you recommend running another Fediverse microblogging software like Pleroma or Calckey? They can use/interact with all Mastodon features just fine. The issues you found…were they Mastodon-specific or Fediverse/ActivityPub in general?
Python's creator and BDfL works at Microsoft.