Okay, so with fish in a tank like that, I bet they love running around all the grassy wavey hiding places, until they hit an open patch and realise its a glass wall.
Plants are not immovable objects. they are not solid. A little likea sponge it looks bigger than its actual mass and therefore a tank filled to the brim and covering the whole substrate still will have 75+ area of space. I've never seen a fish hit the glass looking for open space

If you watch the fish in a planted tank you'll see they spend much more time in the 'undergrowth' than in the open!!! Not for fear although it does add security but for many other reasons. Lots of areas where food gets caught etc. Play chasing each other through the multiple 'chicanes' you get the idea
How would you clean a tank like that? Do you even need to worry about it?
I have no idea what cleaning is apart from water changes and filter cleaning. When I used to do water changes all I did was to close the in/out valves, take the hose connector from the filter and then open over a bucket. Therefore No I don't worry about it
The subtrate, you wouldnt siphon the gravel would you to get rid of fish waste? Do the plants take care of that?
I only used to use the siphone to refill the tank (with the bucket on a shelf above.) Yes the plants (and to a lesser extent the filter) take care of it. I didn't follow the rules of cleaning when I was Hi-tec. I would have gone lo-tec much sooner if I had to do 'gravel vaccing'. I basically ran it as a hi tec tank but with lo-tec procedures on maintenance (except for the 50% EI water changes.)
Lots of flow and circulation prevents the majority of debris falling to the bottom of the tank. Instead it gets sucked into the filter. Which Andy cleans every month I think.
Yes and no here. With the majority of livestock bodymass being bottom feeders most of the waste hits the substrate. Not much went through the water column so not too much in the filter. Just general water born stuff and the little fishies mess
Some may get stuck on the plants but you give them a good shake. Hence, no need to gravel clean, mayber hoover over the substrate once in a while.
This is where the circulation comes in for me. Just as it blasts the nutrient and CO2 around it also keeps plants moving and therefore no time for much to settle. Like I said above. I never followed the general hi tec maintenance. No plant shaking by me

They shake from the circulation....permanently. For the hoovering you can chage 'once in a while' to 'once'. That 'once' was when I first got a tank in 2006
Can everyone give up cleaning their tank under hi tec conditions? Not something I would suggest.
Is it that I am just such a genius? Mayeb but more likely I am just lucky and have the right mixture of fish and clean up crew allied with a fairly decent setup and balance in my tank

Sometimes these things are stumbled upon by pure chance rather than any expert knowledge
what plants do you have they sure are nice
What you see there from the top are Philippine Java Fern with the big leaves and Needle fern with the ong thin leaves.
Just to add to the 'picture tells a thousand words' theme this is about 2 thirds of the needle fern that came out of that 125ltr tank when I broke the scpe down. It sold quite quickly too:
AC