Hello Anders,
I've looked into your question, and as I suspected, it's not possible to enforce a global default folder. However, by using a custom File Explorer shortcut for your personal browsing and relying on "Quick access" within dialog boxes, you can minimize most of the repetitive navigation.
In current versions of Windows, there is no such global setting. These dialogs default to either the last location you used or to the "Quick access" view. That behavior is built into the system and cannot be overridden, at least not by any method I know of. I didn't find a single relevant registry key or group policy setting.
To speed up access in these dialogs, pin your preferred folder and its subfolders to "Quick access". You can either drag them there or right-click and select "Pin to Quick access". Then, whenever the file picker appears, you can reach your folder with a single click from the sidebar instead of navigating through all the folder tree.
Another idea... if you create a custom shortcut (e.g. on the taskbar or desktop) and, in the "Target" box, you enter:
explorer.exe /root,"C:\Users\Anders" (replace with the folder path you want)
that shortcut will always open directly to your folder. Note that this only affects windows you open with that specific shortcut. When an application opens a file dialog (like “Open” or “Save”), Windows will still remember the last location you used.
Best regards. If you have any more questions, feel free to let me know. I’ll be around the Community. If you reply, I’ll try to get back to you as soon as possible. I believe we’re in different time zones, so apologies in advance if it takes me a little while to respond.