Hello, I'm about to install plasma mobile on a Nexus 5X. I'd like to know if there's activation of the GPS functionalities and if there's an interface to use it, such as Osmand for example. This seems to me to be the only function I cannot use with a web browser.
Thanks in advance.

Check out KDE Marble Maps.

I couldn't comfortable recommend Marble to anyone especially since it isn't usable. I do hope someone is eager to make the KDE equivalent of OsmAnd. If I get time, I might look into it.

As someone who contributes to OSM, the most active, Linux mobile app friendly app that I'm aware of (i.e. dev is on both librem5 and Plasma Mobile Matrix channels) is Pure Maps.

https://openrepos.net/content/rinigus/pure-maps

My impression is that Marble has largely dropped off (no blog posts since 2016, Android app removed from Google Play store who knows when). It'd be great if Marble went active again and was mobile friendly and had solid navigation...