There was a Forbes article in May discussing how Ukraine wanted to destroy the bridge but couldn't because it was beyond their capability.

However, cutting a bridge of this size is quite a challenge. The supports are massive concrete and steel constructions, and attacks on similar bridges show they cannot be brought down by anything less than a direct hit with a massive warhead. The USAF’s choice of weapon for bridge-dropping is a series of guided 2,000-pound bombs, and even then success is not guaranteed, as pilots discovered during the 1991 Gulf War

“I thought that bridges would be pretty easy to knock out with PGMs [precision guided munitions]—until I tried it. We would attack a bridge and get several hits, and then we’d discover—holy mackerel!—the bridge was still standing,” Lt. Dave Giachetti, the 48th Tactical Fighter Wing’s specialist in bridge attacks said in an Air Force Magazine article.

The article goes on to say that unmanned robotic boats packed with explosives could do the job, and that the US possibly supplied them with said boats.

https://archive.ph/A80bt

Edit: Also, about 2 weeks ago, a mysterious unmanned drone boat washed up in Omega Bay in Crimea.

SECRET WEAPON Mystery as ‘Ukrainian suicide drone’ washes up on beach close to Russian navy base after evading defences