How do I turn on mock location for the first time?
Settings → “Developer options” → “Select mock location app” → choose Mock Location. After that, just tap the point you need on the map in the app — spoofing starts right away.
This choice is made once: the system remembers which app is allowed to supply coordinates and keeps it until you change it yourself or uninstall the app.
If “Developer options” is not in your settings, you need to unlock it first: Settings → “About phone” → tap “Build number” seven times in a row. On some skins the item is called “MIUI version” or “HyperOS version” — the idea is the same.
On first launch the app itself will tell you what is missing for stable operation and open the right system settings screen — you will not have to hunt for items in the menus.