The largest barrier for me in FLOSS and FOSS applications is simply a lack of GUI tools for what is considered to be "Advanced" functions.

Just because I can do it on linux doesn't mean it's easy or intuitive. Unfortunately a lot of FOSS and FLOSS applications are, of necessity, extremely limited in what tasks they are targeting. Frequently you cannot rely on the "alternative" to have a relied upon function or feature until deep in it's lifecycle; when finally enough people have complained and the feature is implemented.

Sometimes a feature is never implemented due to an entirely shifted paradigm in the way the program is implemented and the feature is "impossible" or "inconsistent with xyz".

One example of this is the number of GUIs and frontends written for ffmpeg; many of which simply are lazy GUI implementations of what the ffmpeg CLI binary itself will helpfully print out in the console when you ask it for help with the correct switch(es). Many are even less thought out than this and will often unhelpfully provide an obtuse box at the bottom for custom commands you wish to feed to the program....which is great if you know the command(s); but make using the GUI unhelpful when compared to just firing up a CLI and reading the output and figuring out the correct command for exactly what you want it to do.

Keep in mind; I am not at all uncomfortable with using CLI interfaces; I just expect that a GUI doesn't force me to fallback, or become so unusable that I am forced to fall back on an original CLI tool because I cannot possibly discern why it failed to work

Frequently things that would be simply be an option buried deeply in the GUI menus only and are otherwise fairly simple are relegated as being only possible within a CLI interface; and I find that reality quite infuriating most often...as the limitations of a CLI oftentimes make the task I am trying to complete far less simple than it really should have been.