I went there a couple of years ago for a conference, stayed on a few days and went biking.
There is or was a bike shop at the cable car that goes up into the mountains I rented a Speccy Big Hit off them and a full face lid. There weren’t any maps available so I just caught the cable car up to the very top. You can see where the trails go and where the lake is and just followed my nose back to the shore. From top of mountain to lake is a good run probably 10k or so with varied terrain some nice techy bits there were lots of Italian riders on full on downhill bikes but unless you went looking for jumps you could ride any of it on a decent trail bike. With a bit of internet searching I found an email address for cable car bike shop they can do guiding but I didn’t bother.
I enjoyed it there I don’t know about XC riding but am sure there is plenty given the terrain the downhill was great and I am not a downhiller I think I came down on a different route each time. There is a cafe about half way down good for some lunch. Take a multi tool as they weren’t too keen on swaping brake levers round.
Stresa is worth looking round lots to see and cafes in the central square are good eating. The small islands on the lake are also worth a look.
Hope this helps.