This sounds more like a mechanical jam or damaged focusing mechanism than a simple autofocus motor failure. Community reports describe similar symptoms when the internal focusing ring/rail was bent or jammed, sometimes after a knock to the front of the lens. That would explain why manual focus is blocked and autofocus clicks but doesn’t move the optics.

Best next step: get a quote from Canon service or a reputable repair shop. If repair cost matters, ask for an estimate before authorizing work.

DIY disassembly is usually not advisable unless you’re prepared to write the lens off. Even if the issue is straightforward, lens repairs are fiddly and may require replacement parts plus precise reassembly/alignment.

One low-risk thing you could try first is gently tapping the lens on a clean surface to see if a minor jam frees up, but don’t force the focus ring.

If the lens was bought used and has no warranty, professional evaluation is still the safest way to confirm whether it’s worth repairing.