Kagi should have a clear policy of how old browsers they support. This is a very common problem within the industry.
In this case they can either polyfill groupBy or write the code differently.
The problem with Safari is that you can’t just ask users to update. The versions are bound to OS version. So for instance, a lot of users are on old iOS devices, locked to Safari 12, which is really old, and Kagi should strategically decide if they want to support these users or not. It is possible, just a bit of extra work.
