If easily means whether there is somewhere a functionality in the UI that allows you to define the font size, other then using Studio, then no.

If easily means globally without editing each template manually, then yes - but you will need to create a module for it and include a style sheet with the style definitions of your liking (plus, probably some template overrides due to static inline style definitions).

If you choose to to the later, here are some resources that may be helpful in achieving this:

• https://www.odoo.com/documentation/18.0/de/developer/reference/backend/reports.html
• https://www.odoo.com/documentation/18.0/de/developer/reference/frontend/assets.html
• https://www.odoo.com/documentation/18.0/de/developer/reference/user_interface/scss_inheritance.html