How do I find a video editing app compatible with macOS Catalina for DV camera uploads?

If that Mac does not have built-in FW, you'd need nowadays hard-to-find FW-to-Thunderbolt adapters to import tapes from a DV/D8 camcorder. The best solution might be to buy such old Mac and the old iMovie v1-6 HD (depending on the macOS). If you already have such adapters, you could use Final Cut Pro for the import and edit (sorry, I have no 1st hand experience from cheaper alternatives). There are also USB converter boxes but I'd check the specs carefully because there are so many flies in the ointment (interlacing, rectangular pixels, codecs etc). Or use some service.

StreetfoodIsKing wrote:

I bought an old Mac because of the thunderbolt cable issue, but iMovie is not on it. Tried to download but current version isn’t compatible with Catalina.

I'd install an older macOS which supports 32-bit apps for DV support, maybe Snow Leopard, El Capitan or High Sierra depending which version that Mac supports. And buy the compatible old iMovie v1-6 for that macOS version from eBay etc.

For example: iLife 06 installer doesn't run on OS X 10.7 or later because it is a PowerPC application. iMovie HD 6.0 can be installed via Pacifist (≈$20): Open the iLife 06.mpkg installer with Pacifist, select the whole iMovie package and let Pacifist install all components to their correct places. iMovie HD 6.0.2 Combo Update and iMovie HD 6.0.3 Update can the be installed normally. OS X 10.9 is the last where iMovie HD 6.0.3 (and 6.0.4) normally runs, or in macOS 10.10-10.14: Right click to show package contents. Open contents. Open info.plist in Text Editor. Scroll down close to the bottom and locate line:

<key>CFBundleVersion</key>

<string>6.0.3<string>

Change the 6.0.3 to 6.0.5.

iMovie HD 6 might be blocked in /System/Library/CoreServices/CoreTypes.bundle/Contents/Resources/Exceptions.plist. SIP needs to be disabled to make changes (maybe change "launch override", to get iMovie HD 6.0.3 to run).

Have you used iMovie, it free and likely already installed on your Mac, also have you looked in the Mac App Store?

iMovie User Guide for Mac - Apple Support