I grow Several Mulberry cultivars. A Good mulberry is one of my favorite flavors. A great balance of sweet and tart. I don’t care for ones that are Sweet only. Morus Nigra species are pretty much accepted as the best, but as Timo eluded to many folks and some nurseries incorrectly state Nigra only based on fruit color. The problem with Nigra is that it doesn’t grow well in many areas including mine. The Humidity in the southeast doesn’t agree with it. I still have a small Nigra Black Beauty alive but it’s smaller than when I initially planted it. I lost a couple other Nigra prior. I have lost 2 Pakistan to cold here in zone 7b. It’s a large fruit and taste is nice but there are others I prefer, but I will likely try to plant or graft it again.
On propagation some cultivar cuttings seem to root fairly readily and others are very difficult or it seems at least for me. Most I found most graft pretty easy but I a couple I obtained failed. I think there are some graft issues between species and you will see some conflicting info on how many species exist and what species some mulberry are.