Suburbia – how to show more blog pages

Hello

I’ve set up a little website:
https://www.questioningcreatives.com/

I’d ideally like to show another row of posts – so 12 in total. At the moment, when I go to: Settings: Reading

I can see a heading that says: Blog pages show at most ‘7’.

I change it to 12, press ‘Save Changes’, but it reverts to ‘7’.

If anyone has any ideas it would be great.

Thanks

James