For end user/consumer software, 90% is nowhere near high enough. In b2b/enterprise settings you have levers to help you push that number higher through IT policy, but end users will absolutely attempt to visit your cutting edge 2022 website on the iPad 3 they've used lightly.

My rule of thumb has been that if it's an app core to someone's job or life management, it needs to be functional for hardware/software going back 5-7 years, less if it's just entertainment or something.