Looking at this page, it seems the "F" applies to "Nasdaq...

Looking at this page, it seems the "F" applies to "Nasdaq International Designation Companies":

Note the requirement below that Companies must be incorporated outside the United States and be listed on a foreign exchange.

https://www.nasdaq.com/solutions/nasdaq-international-designation

In addition to the requirements above

• Companies must be incorporated outside the United States and be listed on a foreign exchange.
• Companies must demonstrate compliance with the standards on its most recent filing with its home regulator or exchange, as applicable, not more than 12-months old.
• For new ADR shares there is not a volume requirement for the first 12-months and minimum market cap is $50M US.