US Airlines: None
BA: None
KLM: None
Virgin Atlantic: None
LOT Polish: None
Brussels: None
Air Canada: Cloth mask, 6+ or 2+ on flights to/from the US.
El Al: Cloth mask, 6+
Air France: Medical mask, 6+
Cathay Pacific: Medical mask, 2+ (No mask required in J/F when in bed mode)
Lufthansa: Medical mask, 6+ or 2+ on flights to/from the US.
Swiss: Medical mask for select destinations, 12+,
https://www.swiss.com/cz/en/customer-support/travel-and-corona/travel-briefing/destinations-masks,
Tap Air Portugal: mask, 6+
Finnair: None
Ryanair: None
SAS: None
Singapore: mask, 6+
Norwegian: None
Tarom: None
Turkish: mask, 6+
Emirates: mask, 6+
Qatar: mask, 6+
Etihad: mask, 6+
Flights any airline to/from China, Italy and South Africa require medical masks by law. (except United doesn't require from South Africa to US)
Post more airlines below and add to Wiki.