Deleted Bootcamp partition space is not unavailable anymore
You have a strange configuration. The drive's disk0s3 is type APFS in the GUID Partition Table (GPT), but does not appear to be APFS formatted. This would explain why the Boot Camp Assistant failed. Hopefully, these commands will fix your problem.

sudo diskutil apfs deletecontainer -force disk0s3
sudo diskutil erasevolume free none disk0s3
sudo diskutil apfs resizecontainer disk0s2 0