I’m not a GFX artist so I can’t comment on the actual model but I do think the background personally strikes me as ‘off’. I think it looks very plain and flat in comparison to the model and it doesn’t really fit the armour being in a sunny field if that makes sense.
A plainer background (just using simple colours rather than scenery) might fit or a landscape which suits the armour would make more sense personally.
Whatever you choose is up to the purpose of the GFX but I think the background as it is now should be improved on or changed - even if it’s just adding some trees in the background to give it more depth.
I think it looks quite good though (but again, I don’t make these), best of luck in future projects 