Not sure about Reaper, but most Windows-only VSTs work fine on Linux using yabridge in my experience. Some DRM can have issues, though, and sometimes you need to install dependencies using winetricks.
Also, I noticed you mentioned using Ubuntu since Mullvad is supported. I have a feeling that you’re attempting to download software through websites instead of using your distro’s repo or by using flathub. Downloading software “the Windows way” by using websites isn’t recommended unless it is not available on repos. Mullvad works on every distro, for example, and is available on most repos.