Planting outside the wall would allow you to retain the space in the garden for other purposes such as your sun trap. A couple of smallish trees could act as a very effective screen and wouldn't need to grow more than a couple of feet above the wall to provide the extra privacy, with little to no effect on the sun.
Another option/something to give you some sense of privacy while you wait for your outside trees to grow is to use 2m thin vertical planks with gaps in between, say those used for outdoor decking. If you screwed small chunks of wood into the brickwork one near the top of the curved wall and one near the bottom, you could then screw the vertical planks onto those so the planks seem to float off the brick wall. The planks would form a curved, vertical screen and you could even get creative with different heights and spacing.
This is interior but you get the idea:
Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
The magnolia could grow quite wide, so if the grassed area outside isn't yours to use or if there are clauses about planting trees out there it could be a problem. If you are able to plant in the grass outside then you have plenty of choice. Personally I would choose something reliable and fairly narrow, then it won't cause issues in the future. A rowan, or an amelanchier perhaps.
Three small trees, set far enough away from the wall so that their shapes are not compromised would look really nice. I don't see the need for a raised bed. And the brick wall is a good feature, better seen through plantings rather than muddled with trellis.
I think you meant me, Liriodendron hasn't posted here. I suggested trees
Dordogne and Norfolk. Clay in Dordogne, sandy in Norfolk.
That magnolia, although slow growing, could eventually grow 10m high and 10m wide, far too big. Something slimmer would be better. There are slim flowering cherries and crab apples.
@Nollie's idea looks rather good too, especially if you like the contemporary look. You could have plants in large pots on the terrace area to soften it.
Dordogne and Norfolk. Clay in Dordogne, sandy in Norfolk.
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The reason I suggested a raised bed is very simple. You get some height much more quickly
I live in west central Scotland - not where that photo is...
https://www.gardeningexpress.co.uk/large-4-5ft-magnolia-rustica-rubra-tulip-tree?fee=1&fep=16490&gclid=EAIaIQobChMI3-iM-rDX9wIVQ-7tCh1l4w26EAQYASABEgJMR_D_BwE
This is interior but you get the idea:
If you are able to plant in the grass outside then you have plenty of choice. Personally I would choose something reliable and fairly narrow, then it won't cause issues in the future. A rowan, or an amelanchier perhaps.
@Nollie's idea looks rather good too, especially if you like the contemporary look. You could have plants in large pots on the terrace area to soften it.
Now am I still young enough to be 'away with the fairies' or was that a senior moment?🤔