If you have downloaded oldclassiccalc-2.0-setup.exe , here is what a legitimate copy looks like:

: Some less-known AVs might flag it as “hacktool” due to its method of modifying system UI preferences. This is a false positive.

oldclassiccalc-2.0-setup.exe is a lightweight, safe, and lovingly maintained tribute to one of the most iconic pieces of desktop software ever created. It boots instantly, respects your keyboard, and never forces you to wait for an animation to finish before typing the next number.

You're interested in the oldclassiccalc-2.0-setup.exe software. Based on my research, here are some good features of this classic calculator software:

Offers various utilities, though not the specific old calculator. Conclusion

Public sandbox analyses, such as those from Hybrid Analysis , generally classify the file as having when downloaded from the official source. However, because it modifies system-level behavior to redirect calculator shortcuts, some antivirus programs may flag it as a "potentially unwanted program" (PUP). OldClassicCalc-2.0-setup.exe - Hybrid Analysis

: Click inside the calculator window to focus it. If still broken, reboot.