"Ad-Free" here is a compound adjective and as such needs a hyphen. The adjectives "Proton" and "Web" both modify the noun "Browser", but "Ad" and "Free" do not. An alternative first-pass reading is "Proton Ad: Free Web Browser", where "Ad" is a free-standing noun, and this is a valid description -- but this is not what is meant.
"Ad-Free" here is a compound adjective and as such needs a hyphen. The adjectives "Proton" and "Web" both modify the noun "Browser", but "Ad" and "Free" do not. An alternative first-pass reading is "Proton Ad: Free Web Browser", where "Ad" is a free-standing noun, and this is a valid description -- but this is not what is meant.