Are there any reliable free antivirus programs for the Mac Catalina?

macOS can take care of itself. Third party AVware will only slow down or bork your Mac.

If you want to check for malware it is best to ocationally use MalwareBites or EtreCheckPro which also checks performance.

https://www.malwarebytes.com/mac/

https://apps.apple.com/us/app/etrecheck/id1423715984?mt=12

Mac OS is EXTREMELY secure and it does not benefit from nor does it require any additional AV apps, cleaning apps or any other third party "maintenance" apps. Most AV apps have the exact opposite effect users want, they make Mac OS slow, unstable and create additional issues with the computer. If simply kept up-to-date and otherwise left alone most users experience years of trouble free problems with their Macs.

Read this article first:

Effective defenses against malware and ot… - Apple Community

Your welcome.