When trying to run the latest dev builds
RawTherapee_dev_5.9-58-g7afdfc1e2_win64_release
RawTherapee_dev_5.9-60-gf49d10c60_win64_release
the following message appears:

RawTherapee_dev_5.9-57-g21afbaf90_win64_release runs fine
When trying to run the latest dev builds
RawTherapee_dev_5.9-58-g7afdfc1e2_win64_release
RawTherapee_dev_5.9-60-gf49d10c60_win64_release
the following message appears:

RawTherapee_dev_5.9-57-g21afbaf90_win64_release runs fine
This is because of libwebp update to 1.3.0 - it now depends on libsharpyuv (which is part of the libwebp 1.3.0 package itself), and needs to also be bundled in the installer.
It has just been fixed: Add libsharpyuv-0.dll to Windows build by Lawrence37 · Pull Request #6672 · Beep6581/RawTherapee · GitHub