There’s a discussion going on in that thread Monzo and the Pride flag from mostly people within the community itself.
The consensus is there’s no consensus. The LGBTQ+ community by definition has no 1 spokesperson or objective narrative. The 6 tone pride flag (roygbp), 8 tone Philadelphia flag (pride plus black and brown), and 11 tone Progress flag (pride plus triangle of white, pink, blue, brown, black) all have different applications and use cases.
In my opinion, the 6 tone pride flag would be the appropriate one here as it’s about a pride flag variant of the card - and aligns with the current colouring of the pride app icon. This is subject to change from debate.