I Have come across such a situation, This article could offer some guidance:How to Remove URL:Blacklist Alerts https://gridinsoft.com/blogs/url-blacklist-avast/ ?
To remove persistent warnings, follow these steps:
Download and Install GridinSoft Anti-Malware.
Run a Full Scan:
This scan checks all system volumes, including hidden folders and system files.
It usually takes about 15 minutes.
By completing these steps, you can identify and eliminate threats, resolving URL:Blacklist issues effectively.