Since updating to Catalina, I found that Time Machine backups to my Synology NAS were very slow and would fail after a long time. I successfully completed a Time Machine backup in safe mode so when an incremental backup started I watched as it slowed down to a crawl. While it was doing that I disabled ESET Real Time Protection and sudden; t backup speed was back up to normal. I've subsequently disabled ESET's checking of network drives, but I hope that someone has a look at why this is happening
I've also posted to Apple discussions and have found many others with the same problem although I don't know what virus cheers they are using.