It’s one of 2 things, normal bumps that just show up as the others have said or it is scale/barnacle/bugs, can be hard to tell as scale tries to mimic the natural growth bumps. Also could be a combination of both.
If plants are looking great and healthy than probably the former and nothing to worry about. If plants aren’t looking too good and having issues than may need to look into it further as plants will be unhealthy with having their life juices sucked out constantly by the scale. Check the leaves (and undersides) for any signs of these bumps, as the normal bumps will not be on leaves, but the scale can.
See if they can be removed by rubbing or picking off the stem, if so than it’s a scale or bug of some sort.
Can also try to blast some off the stems with a spray bottle with water (high pressure stream), if they come off then it’s scale. Can also apply some capt jacks dead bug (or any spinosad based pesticide) and see how the “bumps” react.