Brave won't update on Ubuntu, could antivirus be blocking it?

Yes, check the antivirus event database, not just the usual system logs. Kaspersky Endpoint Security for Linux can report a threat against a file inside the downloaded package even when the regular logs don't show it.

For example, sudo kesl-control -E --query -n 200 retrieves recent events. Look for ThreatDetected, the Brave package path and the detection name. A detection would explain why apt can't open the archive, though it doesn't by itself prove the detection is a false positive.

Since this is a work machine, pass the event details to your security team before making an exclusion or disabling protection. They can verify the package and review the detection with the antivirus vendor.

Cleaning the apt cache is a reasonable first try when a download may be damaged. Run sudo apt clean, then try the update again. If the same error comes back, especially after other packages update successfully, keep looking rather than repeatedly clearing the cache.

The missing control.tar message may just be a consequence of apt failing to open the archive. Check whether the downloaded .deb is still in /var/cache/apt/archives, then try inspecting it with dpkg-deb --info. If it vanishes during inspection, that points toward something intervening at file access, though antivirus is only one possibility until you find an event.

You can also compare the downloaded package against a trusted checksum for that exact Brave version and architecture. A matching checksum helps check that the file wasn't corrupted or changed, but it won't settle whether a heuristic antivirus alert is valid. Don't rely on a checksum for a different release.