Visual difference among H1 and H2 tag is very small. I would like to change H2 to be a bit smaller font size.

Block editor does not offer that to be done on global scale.

Is there way to do this adjustment other than digging through template CSS?

After I installed this theme it started displaying aggressive advertising of commercial version on each and every page in dashboard.

How this advertisement can be shut off, other than buying commercial version?

I believe this kind of advertising is not allowed by WordPress.

I have set two navigation menus and site tile in header of page. Al of them are links and all of them are shown underlined.

None of the block editor options that should disable underline works. There is no option to simply add css to directly change appearance of the item.

How can is remove underline on the links other than directly editing css file?