So would it be valid to say that all transplant recipients have a significantly higher risk of developing cancer ?

Yes, but it's largely because of the lifelong immunosuppression to not reject the transplant reducing the body's ability to combat cancer. Of course, it's still better than not having that organ!

https://www.cancer.gov/about-cancer/causes-prevention/risk/i...

In addition, different organs need different amounts of immunosuppression. Livers are used to filtering random things and thus the body is more tolerant of livers (needs less immunosuppression). Some older liver transplant recipients can actually drop their immunosuppression drugs completely.

The exact transplant protocol also influences long-term levels of immunosuppression and thus cancer risk.

Yes, but not just from the transplant. The immunosuppressant drugs following a transplant also increase your risk of cancer. Dramatically for certain types of cancers.

Well sure, more risk than an individual, less risk than two individuals.