In the British context, the lost courses I detect most love for have been Bramshot (a particular favourite of Henry Longhurst), the New Course at Addington (ditto), the old 9-hole course at Frilford Heath, and the legendary seaside nine holes of the Royal Isle of Wight GC at Bembridge. The estimable
Missing Links has an ever-increasing archive on these
https://www.golfsmissinglinks.co.uk/and I know that whole GCA threads have been devoted to this theme in the past. Personally, I would have loved to have seen the 'proper' nine holes of the Merionethshire Golf Club at Fairbourne ( a founding club of the Welsh GU), extending right out on to the spit opposite Barmouth, and since 1939 Rhyl GC has sadly lost half its holes (and thus its pre-war welsh championship status). It's also a great shame that neither of the courses at Towyn or Dyffryn on the coast between Harlech and Aberdovey has survived either: one fun, short, accessible seaside course would add greatly to the already strong offerings of what Bernard Darwin would have known as Merionethshire.
I went past Potters Bar in the Cambridge - Kings Cross train yesterday. Already a melancholic and forgotten air over the course that,
inter alia, was good as a pub quiz question: identify the Hertfordshire golf club to which Tony Jacklin was attached when Open Champion of both Britain and the USA?