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The traditional approach is to create either a single dotfile, or a single dot-directory, directly under the user's home directory, named for your application. Thus `~/.thromblemeisteradmin` (which could be a plain file or a directory containing any number of files). Sometimes a directory has a name suffix of `.d`, but that is redundant if there's only a directory. If it's a directory and appropriately named, it's generally assumed to be "owned" by the respective application, but entirely possibly under the control of the user.

However, while many applications still do this, **this practice is discouraged** on Linux since quite some time ago.

These days, the recommended location for such data, per the Linux [Filesystem Hierarchy Standard](https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard) version 3.0 ([authoritative standard document](https://refspecs.linuxfoundation.org/FHS_3.0/fhs/index.html)) and the [XDG Base Directories specification version 0.8](https://specifications.freedesktop.org/basedir-spec/basedir-spec-0.8.html) is to, among others (the XDG base dirs specification has a more complete list and is the authoritative reference for the usage of each):

 * store user-specific configuration data in an appropriately-named subdirectory of `$XDG_CONFIG_HOME`
 * store relatively important user-specific data in an appropriately-named subdirectory of `$XDG_DATA_HOME`
 * store relatively unimportant user-specific data, such as current application state or recovery files, in an appropriately-named subdirectory of `$XDG_STATE_HOME`
 * store readily recreatable user-specific data, such as cache data, in an appropriately-named subdirectory of `$XDG_CACHE_HOME`

Each of these will very likely appear somewhere within a subdirectory of `/home`, but you can't necessarily count on that; consider `~root` which is often `/root` or [on some systems](https://en.wikipedia.org/wiki/Root_directory#Related_uses) `/var/root`.

If you really only need a single file for any of these, then substituting a file for the directory is generally acceptable; however, many applications still create a directory, if for no other reason then for future-proofing purposes. So it's not at all uncommon to see something like `$XDG_CONFIG_HOME/<someapplication>/config.ini`, with nothing else under that directory.

As an example, something like a hypothetical SSH client adhering to the XDG base dirs spec might store its configuration somewhere under `$XDG_CONFIG_HOME`, host and user keys somewhere under `$XDG_DATA_HOME`, and optimization data (I'm not sure exactly what that might be, but with the advent of post-quantum cryptography, who knows what might be useful?) somewhere under `$XDG_CACHE_HOME`.