You have no room for worry, as long as these applications run correctly.
The Chrome warnings seem the most worrying for you, but are probably for third-party inclusions in the browser, typically for advertisements.
The mitigation here might have even been that of
blocking JavaScript code that has been obfuscated.
For more information see the article
Windows Defender Exploit Guard: Reduce the attack surface against next-generation malware.
As regarding steamwebhelper.exe, I checked the Task Scheduler and have
not found any mention of it, which means it's running only when the Steam
client is running. It seems to basically be a browser based on Chrome,
so uses multiple processes when running.
It is said to be used for the in-game browser for viewing Store and
Community pages in the Steam window.
As such, it's used for non-essential tasks, and whatever function
that is blocked by Windows Defender doesn't seem to stop it from
functioning well.
I would therefore not worry about these events, as long as these applications keep on working correctly. While it's possible to create exclusions from mitigation for selected applications, the process is complex and an error might inadvertently lower your defenses for other applications as well.