We've just added preliminary support for Roblox files, both RBXM and RBXL. It's still a bit rough around the edges, but should be able to convert geometry to and from Roblox.
For RBXM import try it out here: https://convert3d.org/convert/rbxm
And for RBXL import try it out here: https://convert3d.org/convert/rbxl
As usual you can import any of all the other formats we support, and just export to RBXL or RBXM. You can get started here: https://convert3d.org/convert
Looking forward to your feedback!