Edit and Preview/View different

Hello,

I changed the default text size from 22px to 24px site-wide on my WordPress site (WP 6.5.3).

Although the text is 24px in the Edit view, it is not in Preview or View. The size of the Caption text is correct, but the paragraph text is significantly too small. It looks great in Edit, then when I go to View it looks very different with the text in the body of the post being way too small. I have tried deactivating all plug ins and it made no difference. I have searched this forum for similar issues but can’t find a solution the topics I found.

Can anyone tell me what the problem might be? This is the last formatting issue I have to fix (there have been many), and I just want to get my site live!!

Any help very much appreciate. Thanks everyone