I was going crazy trying to copy 5GB~ of development files to an external SSD in Windows 10 (which I use for some legacy programs and occasional gaming). Extremely slow copy speeds - from 0-400k(ish)/s! And, yes, attempted most/all proposed solutions found online, without success.
Then I booted up my 'travel stick' -- Manjaro installed on a thumb drive -- and rsync'd the same files from/to the same drives at 12MB/s.
So, many thanks! I'd sort of forgotten about Rsync after using it quite a bit several years ago in a homespun backup script.