Can I delete the .dmg files on my Mac once I install the app?
Yes.
You can safely delete .dmg files.
A disk image file (.dmg) is simply an easy, portable structure to transfer an app to you without falling afoul of any internet 'oddities' such as compression, splitting etc. So long as the .dmg arrives intact [&amp; it is self-checking in this regard] then you can be sure it arrived &quot;as sent&quot; &amp; can copy it to your Applications folder. Once you have done that, the .dmg itself is no longer required &amp; can just be deleted.
The only two reasons to keep them would be for:

archival purposes - just in case the original becomes unavailable for any reason &amp; you might one day need to reinstall on a new Mac (if you have it backed up to Time Machine you can delete it sooner of course).
Incomplete installation - some people run apps out of a DMG and don’t install the app drag and drop. In this case, put the dmg in the trash but don’t empty it. Reboot and if you can run the app, it’s safe to empty the trash.