Just a quick PSA:
iOS 15 and iPadOS 15 will officially release today.
I've been testing the betas against the Lionel and MTH apps, and I'm pleased/relieved to report that despite the Legacy and DCS apps not being updated in years, they continue to be functional on the new OS's. YMMV, of course, so test carefully, but the apps have performed identically on 15 as they did on 14 for me.
Rafi