I haven’t tried in this particular case, but they are very backwards compatible and I have had success running some CS professor’s 20 years old random, obscure jar about some datastructure visualization, downloaded from these old, ugly html-only university website.

Not this one but there is a logic gate simulator I used in Uni called Logisim whose JARs (compiled ~10 years ago) continue to work in JRE 21 on my PC.