The Fatsia that I recommended @Fairygirl is unlike the Fatsia japonica which many people grow - it likes full sun! Mine is perfectly happy in the conditions which the OP described😊.
Since about March last year, I think @Fairygirl . It gets sun in the morning and early afternoon, so it's in shade for the hottest part of the day in summer. It sulked for a while but then suddenly started to make an impression! The leaves are matt, unlike F. japonica, and thinner, so they move gently when there's a breeze. Something to add to your list perhaps!
Edited - just done some more research, it probably won't like a normal Scottish winter:
Half hardy - unheated greenhouse / mild winter
Hardy in coastal and relatively mild parts of the UK except in severe winters and a risk from sudden (early) frosts. May be hardy elsewhere with wall shelter or good micro-climate. Likely to be damaged or killed in cold winters. Plant can withstand temperatures down to -5°C (23°F)
Rhus typhina or Rhus typhina 'Dissecta' seem to work well in that sort of container (seen lots like this on Instagram) - in the ground they tend to sucker, but that's not a problem in a container. They are extremely tough trees.
"What is hateful to you, do not do to your neighbour".
I have three half ex whiskey oak barrels, one is a pond, one has Acer Bloodgood in it (from Lidl about 6 years ago) and the other has Laurus nobilis (Bay). All unlined as the oak would shrink otherwise and the rings would drop.
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Not one I've come across though. Have you had it long?
I live in west central Scotland - not where that photo is...
Edited - just done some more research, it probably won't like a normal Scottish winter:
Half hardy - unheated greenhouse / mild winter
I live in west central Scotland - not where that photo is...