Having the 4.3U OS doesn’t necessarily mean anything in regards to softmodding capability. The real limitation is in whether or not your Wii is one of the newer batches that have hardware limits. Even with 4.3U, if you have an older version you can simply downgrade to 4.1 or 4.2 and then carry on like normal but the newer models brick when you downgrade them.
Check your serial number. What are the first 2 numbers after LU?