This can be anything from a microcontroller and various controller ICs to a sprinkling of MOSFETs ... not just the still common 4000-series CMOS logic chips (introduced by RCA in 1968), but ...

For example the 74LVC series contains a range of 5V tolerant 3.3V versions of many 74-series ICs. CMOS And TTL: A Level Shifting Cautionary Tale Comparison of TTL and CMOS logic thresholds with ...