The store version generally has the same access to all files as the installed version.
If you are using Windows 11 I rather suspect that the “Controlled Folder Access” of Windows is protecting writing the files. If enabled (and I think Microsoft enabled this by default at some point) then Windows blocks any write to specific folders, including your users Document, Music etc. folders. “Controlled Folder Access” can be configured in the Settings app somewhere under “Ransomware Protection”.
If that’s the case there should be a notification in the Windows notification area after you tried to save a file with Picard. The notification should give you an option to open the settings. If not you can also go to the settings and search for Controlled Folder Access. There should be a link to the blocking history, which will give you a list of the last attempts of applications trying to write to protected folders. If there are entries for picard.exe you can allow access for that app. Afterwards it should be possible to save with Picard again.
See also Ransomware protection in Windows Security - Microsoft Support
I’m hesitant about adding this, because it is not as simple as it sounds and will likely draw in all kinds of other issues. I’d rather have things work as intended and font settings are picked up automatically on the platform.
Picard uses a GUI toolkit called Qt, which is cross platform (you can use the same code for macOS, Windows, Linux and others). And it actually already is getting default font sizes for the various UI elements based on the platform and user settings.
Problem right now is that the currently used version 5 of Qt has several issues on Windows if the scaling options are enabled (depending on the exact monitor and scaling settings, this behaves differently on different systems). This definitely needs to be addressed and currently it looks like this can be fixed as soon as we move to the new Qt6.
If we enabled this to be configurable we would need to set the fonts for every UI element. It would also require multiple settings for different UI elements (menus, buttons, labels etc.), and on different platforms different elements have same or different length. We’d probably also end up re-implementing platform specific font size detection, which needs to be tested and maintained and likely trigger bug reports about this. We also use some default UI elements for which we might not be able to control the font size for, so we would receive complaints about this as well.
And all this to have a workaround for a bug for Qt on Windows which should better be fixed.