Question malwares

Are the following malware programs that modify, damage, corrupt, or delete various files from your PC? all malware types operates malicious operations in files?

Trojan:Win32/Wacatac.C!ml, Trojan.DownLoader47.36298, TrojanPSW.Rhadamanthys, Trojan.Win32.Agent.xcajyl?

When a free antivirus program like Kaspersky Free and Microsoft Defender Free doesn't have a malware signature database and it doesn't appear in a complete scan, is it still active and all protection barriers have been breached? without signature is dead antivirus?