With all due respect, it wasn’t as uncommon as you may be led to believe. If someone was granted, say, a barony - this would often come with the requirement for that barony to provide the crown with a particular number of Knights. This depended upon the size of the barony - small ones may have been able to supply 5 knights, and larger ones twenty. Nobles didn’t generally have enough family members to distribute knighthoods to in that sense, particularly of the fighting quality it required, and often took most of them from their trusted pool of men-at-arms to do the duty. When one died (as they would), they would just go get another one.
Looking back into my own family history, I’ve found quite a few people who have become knights, or their German equivalent (Ritters). One became so during the first crusade, for the valiant feat of spearing an elephant in the eye and killing it. Another became one after the Norman invasion of England, for services rendered against rebels. Another became a Ritter for Brandenburg for distinguished service in the Hussite Wars. Lesser nobility was much more fluid, typically, than upper nobility. When wars happened, Knights died. None of what my ancestors did remotely compares to the feats of Henry in this game, who basically kills half a thousand men (or more) and pretty much singlehandedly disrupts Sigismunds plans in Bohemia. You’re damned right that person would be knighted.
As for yeomans, they were not nobility, lesser or otherwise. They were just wealthy freemen. The lowest noble title in the HRE at this time was “Edler”. They, as far as I recall, got slightly less land than Knights. This type of title was usually gifted to civil servants, or long-serving military men entering retirement.