I’m having the same issue with my Windows 10 Windows Defender. It says a bunch of the files in the same cache folder are a high threat adware virus. I cleared the cache through History and that does remove them temporarily but they seem to be refreshed automatically by the browser itself.
At first I thought it might have been an outside program and so searched my processes for anything suspicious. Nothing came up but I decided to test if it was the printer causing it so I disabled all that, a real pain honestly for this device, but the cache was still refreshed so I figure it’s part of the browser processes itself. I’ve only had this issue since the latest update.
As far as I can tell it’s not doing anything. I’ve already run my spyware search program and it didn’t recognize those files as anything malicious. It’s possible somehow someone was able to sneak a zero day virus on the latest build of Brave but that seems unlikely since it’s both open source and with how many people examine the beta build before it goes live. That’s part of the beauty of open source. It’s not impossible but highly unlikely.
P.S. Go ahead and tell Windows to kill the threat. It refreshes itself like I said since it’s some of the files in the cache folder like I explained. It will be back within 30 seconds so there’s no point.