There is an entire open-source ecosystem around having direct access to your diabetes data, which predates the commercial availability of things like sharing glucose data live with others. The Nightscout Foundation (https://en.wikipedia.org/wiki/Nightscout) and Tidepool (https://www.tidepool.org/about) are two nonprofit organizations who lead development on open-source products (Nightscout and Tidepool, respectively) which help with this.

While the manufacturer-provided ecosystems function okay, they give you limited data mobility in case you switched to a different diabetes-related product like a CGM or insulin pump. They also introduce a dependency on on a cloud SaaS platform managed by said manufacturer, which can impose limitations, such as not allowing for real-time access to your data (Dexcom requires an approval process to get real-time data from their API: https://www.dexcom.com/webapi) and can have uncertain reliability (Dexcom had a notable outage in 2019, for instance: https://www.wsj.com/articles/diabetes-blood-sugar-data-outag...).

Conversely, you can run a Nightscout server on a Raspberry Pi in your home, or on a cloud server, for yourself and have full access to your data.