I've developed for x86, and deployed on x86. Some years later we decided to add arm support. Fixing the only on arm bug made our x86 software more stable. Turns out some 1 in a million issues on x86 that on arm happen often enough that we could isolate them and then fix them.
Thus I encourage everyone to target more than one platform as it makes the total better. This even though there are platform specific issues that won't happen on the other (like the compiler bug we found)
Apparently Apple had macos working for years on x86 before they switched their computers to intel CPUs. The justification at the time was exactly this - by running their software on multiple hardware platforms, they found more bugs and wrote better code. And obviously it made the later hardware transition to intel dramatically easier.
I would be surprised if Apple didn’t have internal prototypes of macos running on their own Arm chips for the last several years. Most of the macos / iOS code is shared between platforms, so it’s already well optimized for arm.
Thus I encourage everyone to target more than one platform as it makes the total better. This even though there are platform specific issues that won't happen on the other (like the compiler bug we found)