Since Microsoft ended support for Windows 7 in 2020, you may need to manually download older versions of the Minecraft Launcher. The MultiMC or Prism Launcher alternatives often work better with Win7 + OptiFine.
Because OptiCraft is a modified client, antivirus software may flag it as a "false positive." It is recommended to scan files through services like VirusTotal before installation. Opticraft-WL - Minecraft Modpacks - CurseForge opticraft minecraft windows 7