KINGMAV, also listed as Kmav17, publishes separate single-player and FiveM versions of 2021 Modern Mansion. Select the intended package from the version list; the main download label identifies the SP release.
FiveM installation scope
The documented server folder is 21MODERNMANSION_5M. Extract that resource into resources and use ensure 21MODERNMANSION_5M. The creator specifies game build 2699 and also mentions 2802. Check the package requirements against your existing stack before changing the enforced build.
Single-player requirements
The SP instructions require Map Editor and Map Builder 2.2.3, plus the supplied VG PROPS and 21MODERNMANSIONX.xml. The DLC folder is 21modernmansion; the XML uses scripts/Autoloadmaps. Follow the complete creator instructions for archive paths and back up dlclist.xml and affected archives before editing.
Do not apply the SP OpenIV procedure to a FiveM server. Test the selected edition for missing props, floor collisions, entrances and nearby map conflicts. Retain the original package and restore the previous files if those checks fail.