I’ve had rims that stayed perfectly true for the entire life of the bike. And I’ve had rims that needed to be trued yearly. However, most of my bikes have wheels that are just slightly out of true and I just leave them that way until they are noticeably out of true. When they get to that point, I get them trued at the shop. In my experience, the narrower the rim, to more likely it needs to be trued. I don’t think that I’ve ever had to true a rim that was inner width i30mm or wider.
Love the question. Mine are slightly out of true. If they get any worse I’ll have them trued the next time I need to bring the bike in to the shop. Before I swapped out my stock rims on my XC bike the wheels needed to be trued 3-4x per year and I was set on learning how to do it myself. But after I upgraded my wheels I find that they only need to be trued about once per year so I don’t have the same motivation I did previously. And since I usually take my bike in to the shop at least once a year anyway I just ask them to true it when I’m there.
My front wheel is true and my rear wheel is slightly out. I take it to the shop, but I’m slowly learning and adding bike knowledge and tools, so I hope to figure out how to do this for myself eventually.