The sandbox are using XRv 9000 (check the sandbox for the versions), as far as i know BFD is possible on this platform, however check which features of BFD are possible via the documentation
You could enable BFD in the XR Always-On sandbox, but as this is standalone sandbox and does not connect to anything. If you are looking to see this working, i would recommend the CML sandbox (this uses 7.2.1).
Hope this helps.
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