There will be three versions of the Starship (BFR), a crewed version, capable of carrying 100+ passengers, a tanker version, for refuelling for missions beyond LEO, and a cargo version, capable of carrying up to 150,000kg of cargo to LEO.
What I've yet to see any details yet on is the carrying capacity of the cargo version, apart from an estimate of the weight limit.
The Space Shuttle had a cargo bay 18.3m long and 4.6m wide. Hubble itself is 13.2m × 4.2m (minus solar panels) and weighs about 11,000kg.
Starship is currently expected to be 9m in diameter, and 55m long. We don't know how much of that volume will be taken by fuel tanks, but at least half seems likely, since it has to be able to fill up with enough to get from LEO to Mars. It will also need sufficient heat protection mechanisms will reduce the internal volume, but it does seem likely that there will be enough space to hold the space telescope.
It's also not clear how the cargo space will be accessed. I would suspect it will be more like the cargo bay doors on the space shuttle than the fairings on a Falcon rocket. It will at least need to close to be aerodynamic on reentry, and it will most likely only give access to the top half, as the bottom half will have to have the heat protection system.
However, it does seem likely that there will be enough cargo space to fit the telescope.
The next question is will it be able to land with 11tons of telescope in the hold? Well the crew version needs to be able to land with 100 people (presumably with their luggage). I would think we would need to allow at least 100kg per person, which would be 10,000kg in total, but you can't just throw people in the hold, you need hardware for life support, space toilets, seating, etc. I expect a conservative estimate of 50kg per passenger would be needed over the cargo Starship, so that would mean it would need to be able to land with at least 15,000kg in the hold, more than enough for Hubble.
Another important consideration is how you get Hubble into the hold, and how to secure it for landing (perhaps a big roll of bubble wrap). The Shuttle had the handy Canadarm to grab and manipulate, and it still needed a crew to control it. You would need to grab the telescope, detach the solar panels (and make sure they deorbit and don't become space junk), and secure the cargo safely for reentry, where it will need to withstand forces that probably weren't considered when it was originally designed. The Smithsonian won't be happy if it arrives broken!
Finally there's the question of should we? Would we be better off continuing to service it and keep it operating? Is there more useful science we can get from Hubble, or will James Webb have made it obsolete? Would the money spent retrieving it be better spent on a future space telescope? If space tourism takes off, should we leave it in orbit for future space tourists to see, perhaps hooking it up to a space hotel?