The new Magic Keyboard for the 2018/2020 iPads Pro is not compatible with your iPad Pro 10.5”.
However, if seeking trackpad and external keyboard for your iPad Pro 10.5”, you might alternatively consider the Magic Trackpad 2 and one of the standalone Apple Magic Keyboards:
Magic Trackpad 2 - Space Grey
https://store.apple.com/uk/xc/product/MRMF2Z/A
Magic Trackpad 2 - Silver
https://store.apple.com/uk/xc/product/MJ2R2Z/A
Magic Keyboard with Numeric Keypad - British English - Space Grey
https://store.apple.com/uk/xc/product/MRMH2B/A
Magic Keyboard with Numeric Keypad - British English - Silver
https://store.apple.com/uk/xc/product/MQ052B/A
Magic Keyboard - British English
https://store.apple.com/uk/xc/product/MLA22B/A
You might also consider an Apple Magic Mouse 2:
Magic Mouse 2 - Space Grey
https://store.apple.com/uk/xc/product/MRME2Z/A
Magic Mouse 2 - Silver
https://store.apple.com/uk/xc/product/MLA02Z/A