You did not mention your Archicad version so I suppose you are using Archicad 24.
Download and install the RFA & RVT Geometry Exchange Add-On from the following web page:
https://graphisoft.com/downloads/addons/rfa
If you are using AC21-23, the Add-On can be downloaded from:
https://bim6x.com/store
Then in Archicad, go to the 3D Viewpoint and use the Save As command, and the RVT file format will be available in the "Save as Type" field. The RVT file saved from Archicad 24 will be in Revit 2020 (in earlier Revit versions from earlier Archicad), which you can open in Revit 2021.
Revit will convert any earlier Revit version file to Revit 2021 format the first type it opens it and then it can only be saved as Revit 2021 version.
Another option is of course to export the Archicad 3D model to IFC format and open that in Revit 2021. Would be an interesting comparison to see which method converts the geometry and parameters better to Revit.
(It may be a good idea for you to specify your Archicad version and computer configuration in your signature so we can help you better.)
Loving Archicad since 1995 - Find Archicad Tips at x.com/laszlonagy
AMD Ryzen9 5900X CPU, 64 GB RAM 3600 MHz, Nvidia GTX 1060 6GB, 500 GB NVMe SSD
2x28" (2560x1440), Windows 10 PRO ENG, Ac20-Ac27