There was stagnation after the fall of the Roman Empire while new states and systems were trying to establish itself. However the later medieval period was full of innovation. It was far more active in using machinery than Roman Empire and China:

https://erikexamines.substack.com/p/the-european-mill-revolu...

Medieval Europe significantly advanced glass making, invented spectacles and lenses, laying the groundwork for telescopes and microscopes:

https://erikexamines.substack.com/p/glass-the-substance-of-s...

Medieval Europe pioneered mechanical clocks which was a pretty big deal: https://erikexamines.substack.com/p/the-missing-chinese-mech...

Medieval Europe also advanced gunpowder weapons more rapidly than in China, and already had evolved technology around plate armor and crossbows far beyond anything the Romans did: https://erikexamines.substack.com/p/why-did-europe-and-not-c...

The idea that no innovation happened in medieval Europe is severely overstated. I think it stems from the fact that medieval Europe had less production of literature, science and arts than Rome and Greece. Yet in terms of practical inventions, medieval Europe, did a lot more.