On my old 2.0HDI peugeot mine got to a point where i couldn’t get above 40mph. As you say it had no oomph what so ever. It however was not going into limp home mode and was showing no erros on the dash. even plugging into Peugeot Planet showed nothing.
As others above have said, i assumed the turbo was shot so i started to remove bits from the engine bay to get a better look. As i was removeing all the trim round the back of the engine, i discovered the air intake pipe between the air inbox and turbo had come apart. This meant that air was being sucked in after the MAF sensor so less air was coming across the MAF so it wouldn’t fuel. As soon as i put it all back together and made sure the circlip was tight, it was back to normal.
Could be worth spending half an hour tracing all the pipes on the intake system on both sides of the turbo and intercooler to make sure nothing has come apart or split.
Nothing to loose!! – Good luck