By default windows is now (2025) launching TOPAS with “normal” priority. This can significantly slow refinements down. If you want to launch with high priority you can do this from a cmd prompt or bat file. The syntax is:

start “” /high “c:\YOUR-MAIN-TA-DIRECTORY\ta.exe”

VS Code topas-editor will do this by default from release 1.0.16 for TA.exe and topas.exe (academic and commercial, respectively). It doesn't do this for TC.exe.

Alternatively you might be able to right-click on the program and “Run as administrator”.