I know that Holland said he'd be making more movies without Marvel but I'm going to throw my own speculation out there. I wouldn't be surprised if that whole MCU no longer making Spidey movies was all a massive publicity stunt.
Why do I think this? Because Holland told Hollywood Reporter back in 2016 that he was signed on for 6 films. Call me crazy if you want but it would be very weird to have him sign on for 6 films and for that 6th film not to be MCU based.
The 'Spider-Man: Homecoming' star's Peter Parker isn't a rehash of those who have come before: "I think the biggest difference is his youth and innocence."
www.hollywoodreporter.com
*EDIT*
And I stick by my statement that Sony can't use MCU characters without Marvel's approval. And why do I think that? Because if Sony could use any of the Spidey based MCU characters as they please, they could have put characters from the MCU in Venom but they did not. The new deal that was made allows them to use MCU characters which is why Toomes is in Morbius.
And again, I wouldn't be surprised if Toomes is a last minute addition during re-shoots after the deal was struck.