The sounds in the Soundly Pro and Soundly Free libraries are cleared for commercial use, including video games. Games created while subscribing to Soundly Pro stay cleared even if you end your subscription.
If you add the Freesounds library, be sure to choose CC0-only to only see the sounds which are available for commercial use and that do not require attribution. If you already have added the library, you can choose CC0-only by right-clicking on the Freesounds library in the sounds panel within Soundly
All other add-on libraries are cleared for commercial use.