I have just asked again to Wise support.
According to their support, they only allow to receive money from a platform that is regulated and/or supervised in the EU or UK. Xapo may or may not fall into that category. When you search for Xapo in FCA website, it says that "This firm is regulated in another European Economic Area (EEA) country and can offer certain products or services in the UK." This may not be enough.
Anyway, sending to Xapo seems to be forbidden in any case.
In another message, Wise support wrote me more clearly that they would not allow transfers to or︀ from Xapo Bank if it deals with crypto transactions. Since Xapo Bank does...
My conclusion︁ is that it is very risky to use Wise to send to or receive from︂ Xapo Bank. Wise might decide to suspend or close your account for such use.