Brand New macbook air can't handle simple video editing

It is unusual. Please determine if the same problems occur in "Safe Mode": Use safe mode to isolate issues with your Mac. A Mac is not very convenient to use in that mode for any length of time but it should not freeze or require you to force-quit anything.

Something just isn't right with that Mac. Audio might not function in Safe Mode but freezing is not normal, and may indicate a hardware problem.

Before coming to that conclusion, consider using EtreCheck, which will preclude having to ask a dozen or more follow-up questions and equally time-consuming answers: Using EtreCheck - Apple Community explains what it is and how to attach its report in a reply to this Discussion—you have to use the "additional text" icon shown below:

Run EtreCheck after restarting your Mac normally (not "Safe Mode") and after using it normally for at least a little while, before it freezes. Also, you have to give it "Full Disk Access" which its instructions explain.

I tend to doubt it, because although uploading files to iCloud might affect internet communications it should have a negligible effect on your Mac's performance. EtreCheck will almost certainly provide some insight, or provide more justification for suspecting a hardware problem. The more information you can gather on your own, the better off you'll be when you contact Apple regarding that Mac's performance—which you'll probably want to do anyway.

When you're done with EtreCheck you can just drag its app icon to the Trash. It needs no uninstallation procedure.

Or just leave it be. It does exactly nothing unless you're actively using it.

Posting the report the way you did is correct. I think you will want to avail yourself of Apple's 90 day complimentary telephone or chat support, since that's included in the price of your new Mac anyway.

Until then see if the freezing occurs if you use iMovie and don't use the Mojave Video Editor. Along the same lines of thought is to seriously consider whether you really want Google installed on your Mac. I know a lot of people like it, but you have to decide whether you like it enough to tolerate its effects. Its sole purpose is to continuously scour devices for your personal information and sell it to others. It's not a very good search engine or browser any more, but if you are required to use it then you must remain forever aware of its potential to cause performance degradation. Just something to keep in mind.

Stuck iCloud - This machine has a large number of pending iCloud transfers.

That may in fact be a contributing factor. I don't know the parameters by which EtreCheck concludes those transfers become "stuck" but once all iCloud content finishes synchronizing that entry should disappear. When it does determine if you can correlate the freezing and related performance degradation to it.

Sure. Fifteen minutes ought to be enough to draw a conclusion.