There are OSS solutions for glucose monitors and even insulin pumps, and they exist precisely because commercial vendors tend to give at best suboptimal quality even when it comes to medical devices. Sure, most pay attention to not accidentally kill you, but beyond that, their incentives go in opposite direction to your incentives.

It's important to have computing freedoms so that people who actually care end-to-end, and don't have financial incentives directed against patients' well-being, are able to build on top of products on the market, fix the enshittification, and improve functionality.

(We also need that to close the loop. It's a common story that meh products of today, which improve on bad products of yesterday, are just commercializing the fixes developed by people fed up with said bad products.)