Formal attire has evolved over the years, to the point where the line between smart & casual is blurred. There are still some time-tested diktats you should stick to, however.
Cocktail Attire for Men Guide, According to Style Experts
20 Rules Every Gentleman Should Live By in 2022
20 Rules Every Gentleman Should Live By in 2022
The Complete Guide to Business Casual Style for Men
Wedding Dress Codes: A Complete Guide to Guest Attire
Formal Attire Guidelines & Rules All Modern Gentlemen Should Know
Decode the Dress Code: Business Casual — The Wardrobe Consultant
11 Unspoken Suit Rules for the Modern Gentleman
Wedding Attire for Men: Complete Guide for the Big Day
Different levels of formality (for men) : r/coolguides