We tested ESET Internet Security 14.2.19.0, F-secure safe 18, Trend Micro maximum security 17.0.1299 with WiseVector StopX in Win10 21H1 Pro X64, no problems found.
What we tested?
.Realtime-protection
.HIPS
.Web Protection
.Firewall
It should be noted that if a malicious program is blocked by one AV, the other AV may not have a chance to check it. In addition, after installing the second AV, it is best to restart your computer.
Performance: WVSX+ESET > WVSX+Trend Micro > WVSX+F-Secure > WVSX+Bitdefender. If you want a combo, ESET + WVSX is recommended.
For BitDefender, it feels like installing another OS on top of Windows.
@gery79