Chalk me up as one of the people who may have developed it or speeded onset from one loud concert - that wasn't really all that loud. Late November 2023, attended a concert at one of our intimate local venues, came down with tinnitus about a week and a half later, just before my 65th birthday.
Probably/mostly age-related but I'm certainly more careful about concerts now. I mostly listen at moderate to low volumes with my home setups and with headphones.
By the by, if one does develop it, go and have a full evaluation. There are some nasty things that can be the cause, and it's better to know early. In my case, it seems due to a mild loss in sensitivity in the 1,000 - 4,000 hz region in my right ear. The tinnitus is continuous, I've mostly acclimated to it, but it certainly is annoying. It fascinates me how it can become more noticeable or less noticeable through the day depending on my concentration, other ambient noise, music etc. But ears are like any body part to me - when you really study the wall chart, you have to say, "how does that contraption work at all?"