"geoSearch" is currently allowed inside multi-document transactions on non-sharded collections. So I think we should also support that in non-transaction snapshot reads. This should mostly just work. But we will need to attach the timestamp selected as the atClusterTime in the command response, similar to SERVER-47688.

EDIT: The geoSearch command is deprecated. Thus, we will not add any more features to the command but ban it from snapshot reads instead.