Since leftsider64.dll is not a Microsoft file, reinstalling the original software is the safest fix.
: A reliable source for legacy customization tools. leftsider 64 .dll download
If you are seeing error messages related to , you are likely trying to customize your Windows experience, specifically moving window control buttons (minimize, maximize, close) from the right side to the left, mimicking the interface of macOS. Since leftsider64
: Because Leftsider "hooks" into system windows to move buttons, some security software flags it as a "Trojan" or "Riskware." If you trust the source, check your antivirus chest/quarantine to see if the file was blocked and restore it. specifically moving window control buttons (minimize