It seems that, in general, most camera makers have been content to trade most, but not quite all, of the gains they've made in terms of sensor efficiency in exchange for more megapixels with roughly the same overall performance with regard to signal-to-noise ratio as their older, lower resolution sensors had.
There are some notable exceptions in terms of specific models. But when that is the case, there are often two similar models offered, one with higher resolution that means lower SNR at the sensel (pixel well) level and the other with lower resolution but larger sensels with better SNR for each discrete photosite.
Take for example the first generation Sony α7 model line, which had three different versions:
- The high resolution α7R has a 36.4MP full frame sensor
- The balanced α7 has a 24.3MP FF sensor
- The high sensitivity α7S has a 12.2MP FF sensor
The second generation of the α7 model line was similar, with 12.2MP, 24.3MP, and 42.4MP sensors inside the α7S II, α7 II, and α7R II, respectively. So far we've seen two models in the third generation: the 42.4MP α7R III and the 24.3MP α7 III.
Note that often manufacturers will continue to use sensors that were "cutting edge" when introduced in an upper tier model. Later models lower in their product range will get what is essentially the same sensor. Perhaps the classic example would be the 18MP APS-C sensor first introduced by Canon in their original 7D back in 2009. It has appeared in numerous models since, including the basement entry level Rebel T6/1300D that was rolled out seven years later in 2016.