The point is that Revelation 20 can't be used to define what the sea means in Revelation 21:1.
If we factor in the following since it appears to be involving the same age Revelation 21-22 is involving, this should at least mean we are not to take it as a literal sea in Revelation 21:1.
Ezekiel 47:6 And he said unto me, Son of man, hast thou seen this? Then he brought me, and caused me to return to the brink of the river.
7 Now when I had returned, behold, at the bank of the river were very many trees on the one side and on the other.
8 Then said he unto me, These waters issue out toward the east country, and go down into the desert, and go into the sea: which being brought forth into the sea, the waters shall be healed.
9 And it shall come to pass, that every thing that liveth, which moveth, whithersoever the rivers shall come, shall live: and there shall be a very great multitude of fish, because these waters shall come thither: for they shall be healed; and every thing shall live whither the river cometh.
10 And it shall come to pass, that the fishers shall stand upon it from Engedi even unto Eneglaim; they shall be a place to spread forth nets; their fish shall be according to their kinds, as the fish of the great sea, exceeding many.
11 But the miry places thereof and the marishes thereof shall not be healed; they shall be given to salt.
12
And by the river upon the bank thereof, on this side and on that side, shall grow all trees for meat, whose leaf shall not fade, neither shall the fruit thereof be consumed: it shall bring forth new fruit according to his months, because their waters they issued out of the sanctuary: and the fruit thereof shall be for meat, and the leaf thereof for medicine .
What I have underlined above compare with some of the following I have underlined below.
Revelation 22:1 And he shewed me a pure river of water of life, clear as crystal, proceeding out of the throne of God and of the Lamb.
2
In the midst of the street of it, and on either side of the river, was there the tree of life, which bare twelve manner of fruits, and yielded her fruit every month: and the leaves of the tree were for the healing of the nations .
Then note what Ezekiel 47:8 records---These waters issue out toward the east country, and go down into the desert, and
go into the sea : which being
brought forth into the sea , the waters shall be healed
Obviously, the sea meant in verse 8 is meaning in the literal sense. Which then means if these accounts involving Revelation 21-22 and Ezekiel 47:6-12 are pertaining to the same era of time, we know from Ezekiel 47:8 that the sea meant in Revelation 21:1 can't be meaning in the literal sense, since Ezekiel 47:8 is clearly contradicting that if we decide to take 'sea' in Revelation 21:1 in the literal sense.
In the event that you or anyone else disagrees that Ezekiel 47:6-12 is involving the same age Revelation 21-22 is involving, one then has to get around this then---neither shall the fruit thereof be consumed(Ezekiel 47:12). Where that obviously requires an age that is never ending in order for it to never be consumed. When it says neither shall the fruit thereof be consumed, it is not meaning because no one will be eating any of it. It is meaning because there will be a never ending supply of it which then requires an age that has no end. Clearly, the new heavens and new earth will have no end.