Direct Neuro Input
You've kind of painted yourself into a corner of inevitability with this particular detail:
and extra robotic appendages are ubiquitous.
This fact means that the ability to hook a person's nervous system into a machine that can do stuff that our biological nervous system is not already designed to do has become ubiquitous. So just like you can give someone a 3rd robotic arm, there is nothing left preventing you from attaching a computer to a person's nervous system and allow it to respond in detail to our thoughts.
The reason I say this is inevitable when you reach this level of tech is because you no longer get any lag time or inaccuracy between your thought and your body's somatic response to that thought. You can literally "type" at the speed of thought (maybe even faster with some AI autocomplete features). You can perform pixel perfect interactions with your software because you don't need your crummy eyes and limited motor skills to tell the computer the exact path you want to draw.
Heck, you won't even need the idea of buttons or voice to speak because you will be able to just think about what your options are and make them happen. In this way, checking your email or doing a Google search is going to feel like remembering something you already know or a lucid dream where things you need are just kind of there when the need arises, and learning to do complex tasks that perform dozens of parallel operations could be as simple learning to control all the muscles in your hand to work together to hold your morning coffee.
The question then remains, not if this is the best tech for your civilization, but how to make it flashy:
Cyberjacking

Probably the most interesting version of direct Direct Neuro Input is cyberjacking. This is where you basically install a bunch of plugs into a person (usually depicted on the neck or head somewhere) and you literally plug in. It creates a visually interesting interface even if you can't see what is happening on the inside of the person's head.
The problem of course with cyberjacking is that so much tech is wireless these days that it raises the question about why you would not just have an internal wireless device installed in you. So if go this route, I'd suggest some deep cultural problem should exist for not going wireless like wide spread brain hacking or oversaturation of wireless frequencies or needing data connections that are too complex and data intensive for wireless to be practical.
Non-Perceptual Experiences
This may be hard to pull off in certain mediums, but if this is for a written story or you have a narrator/inner voice, then the lack of sights and sounds can become interesting unto itself. Explaining how your interactions with your computer are literally thoughts, you could make things very interesting.
Responsive Interfaces
One of the biggest software interface trends in the past 10 years has been the idea of responsive design. The way a program looks on a phone can be very different than on a touch screen tablet, which is also very different than for a PC. Likewise, software in this world may need to be responsive to thinking styles.
Sometimes people think in words, sometimes in vague concepts, sometimes in pictures, and sometimes our thoughts are purely subconscious or instinctive... so the user experience of a program might actually adapt to a person's mentality which could lead to some very interesting experiences like the software changing how it looks, feels, sounds, and responds along with a person's emotional state or level of focus. It also means that two people using the same program may have 2 very different experiences.
Behavioral/Cultural Anomalies
Ever see a musician listen to a song they like and they mime out the song in the air like they are playing it? Well people who were born before neuro-jacking was commonplace may do the same thing. Your elderly may still mime out mouse and keyboard or cellphone gestures while controlling thier computers, while younger people may just stand with their hands to thier side without any bias that thier hands are needed to do anything. This will become an "old folk behavior" that may get ageistly mocked. "Ugh! grandpa, you don't need to envision a keyboard to message people."
You may also notice something similar to the echo chamber effect where people who think one way will get software that adapts to thier thought style which then reinforces that thinking style for them. Visual thinkers become radical visual thinkers, verbal thinkers become radical verbal thinkers, etc. This could cause a general increase in neurodivergence or intensify certain psychological disorders.
Henderson explained that he and his colleagues had been developing a brain-computer interface: an experimental connection between someone’s brain and an external device, like a computer, robotic limb or drone, which the person could control simply by thinking.
(Source) Brain-controlled computers already exist (if not to the extent you want, yet). That trumps every other answer you're going to get unless you can define what "fun and flavorful" means in the context of a best answer. $\endgroup$