iPhone 11 isn’t too old! The problem is that Arc records a very large amount of data - much more than any seemingly similar apps - so when you load a monthly or yearly timeline view it’s a lot to load into memory, and sometimes that makes iOS angry and results in iOS terminating the app.
Those monthly and yearly timeline views / map views were added to Arc before the iPhone 11 existed, so they were tuned to be usable on those phones. But iOS is also quite easy to upset, so if you swipe back through years quickly (or even monthly views quickly, if there’s a lot of data in them) iOS is liable to say “nope, enough of that” and kill the app.
If you notice it loading slow, and really don’t want to lose your place by the app being terminated, then it’s best to wait a little bit to give iOS and the app a breather. That will avoid the app going over any of iOS’s “high CPU use within the last 60 seconds” thresholds.
New release very soon! The main new feature is the ability to import location data from recorded workouts (walking, running, cycling, etc). So for example if you go for a run without your phone, but record the run on an Apple Watch, there will be location data that can be imported into Arc’s timeline.