The next GP round is coming up, with the Russian GP authored by Andrey Bogdanov. One of the types is Yin-Yang Fences, which I first saw on Andrey and Vladimir’s round for the Budapest 24 hours this year. You should be able to find these here. Berni made another for our croco 24h review series.
You can leave out one of the 2s on the outside if you want more of a challenge.
Rules Solve as a standard Slither Link. In addition, all cells outside the loop must be connected, and there must be no 2×2-square of cells that is entirely inside or outside the loop.
Or see the instruction booklet.