A large-scale Scintillating Fibre Tracker has been developed and constructed for the current LHCb Upgrade 1. The high radiation by fast neutrons reduces the light yield of the detector in the course of LHC Run 3, and is challenging the tracker's hit detection efficiency. To mitigate radiation-induced ageing effects, the central fibre mats and photodetectors will be replaced during the next long shutdown (2026-2028). For this purpose, microlens-enhanced silicon photomultipliers with an improved photon detection efficiency are being developed. The first prototypes have been produced based on the outcome of dedicated simulation studies, and the results of the first light yield measurements are presented.