Articles and titles are underlined.

There’s a new default styling that adds underlines to links that don’t have the wp-element-button class attached to it. The rule causing this is targeting a:where(:not(.wp-element-button)).

https://github.com/WordPress/gutenberg/issues/44166

a:where(:not(.wp-element-button)) {
    text-decoration: none;
}

To add or override CSS: use the “Additional CSS” option in the customizer.? https://codex.www.ads-software.com/CSS#Custom_CSS_in_WordPress or at [site]/wp-admin/customize.php if you don’t have that menu option.

Use the Chrome Developer Tools or Firefox Developer Tools to help you see and test changes to your CSS.

Solved. Hope the future updates will not bring problems again.
Thank you very much.