The fifth-generation of mobile network (5G) and beyond requires optical-wireless convergence to cope with the new value-added applications from challenging scenarios. In this context, we report research activities conducted at the National Institute of Telecommunications (Inatel), Brazil, concerning the use of microwave photonic techniques for next-generation fiber-wireless (FiWi) systems. It includes analog radio over fiber (RoF) solutions toward multiband and photonically amplified fronthaul, simultaneously transporting microwaves and millimeter- waves in accordance to the 5G New Radio (NR) standard. The RoF techniques under discussion exploit single and dual-drive Mach-Zehnder modulators, wavelength division multiplexing (WDM) overlay, in addition to the four- wave-mixing (FWM) nonlinear effect. The integration of an innovative flexible-waveform 5G transceiver in a passive optical network (PON) infrastructure, from a commercial Internet service provider, is reported. Experimental results demonstrate Gbit/s throughput and error vector magnitude (EVM) in accordance to the 5G NR Release 15 requirements, as well as the coexistence of legacy and incoming technologies in the same FiWi architecture. Experimental results demonstrate also RoF links with power increase of about 15 dB at the photodetector output by taking advantage of FWM. Such photonics-assisted gain is uniform, stable and ultra-wideband, being valid for baseband and radiofrequency (RF) signals in both 5G NR frequency ranges (FR1 and FR2). The approaches addressed in this work are potential to favor the 5G deployment and may contribute to the sixth-generation mobile systems (6G) design.