Is it ok to use the sunbed after cataracts surgery?

Sure. Some lenses used in cataract surgery do not have uv protection. You will still need to have protective eyewear. Otherwise, there are no contraindications.
Cataract. I typically recommend people take it easy for a few days after surgery. Often times the eye can remain dilated which will let in more light when using a sunbed. I agree with the other poster that eye protection should always be worn when sunbedding.