I want to ask if this map of Beleriand (in the northwest of Middle-earth) is correct. I think it isn't because Beleriand should've been sank, and you can clearly see that there is Beleriand above Eriador, but still this is the best full map I've found on the Internet.
First of all, the map appears to be completely unreliable not because it was not designed by Tolkien himself, but rather because its author tried to put together a "composite" map representing all "the lands of Arda throughout the ages", which is an impossible task to achieve.
So, the map shows:
- the two Great Lamps of the Valar Illuin and Ormal, long destroyed by Morgoth and ruined with the surrounding lands before the First Age started;
- Beleriand, which sank beneath the sea at the end of the First Age during the War of Wrath, which also heavily changed other regions of Middle-earth;
- the continent of Númenor, raised at the beginning of the Second Age and then submerged again (with the exception of its highest peak) at the end of that age;
- the Undying Lands, removed from the Circle of the World after the destruction of Númenor;
- parts of Middle-earth as they appear during the events of The Hobbit and The Lord of the Rings (at the end of the Third Age).
To make a silly comparison, it's as "reliable" as a map of Earth showing together Pangaea, Atlantis and present-day Europe :-).
Moreover, as commented by user @suchiuomizu, Númenor appears completely different from the map published in Unfinished Tales (redrawn by Christopher Tolkien from a sketch of his father's), where Númenor is shown as a large star-shaped continent whose central region is a large plain with an isolated mountain.
I'm afraid the map you posted in your question is not a genuine map by Tolkien. The nearest Tolkien got to making a "full" map of Arda is a rough sketch, shown in the original form, ("Map V" in "The Ambarkanta", The Shaping of Middle-earth, volume 4 of The History of Middle-earth) and below coloured for clarity.
The Undying Lands are on the left, and Middle-earth is top centre. This is the world as it would have been before the Breaking, when the world was made round and Valinor removed from the physical world.