I made this polygon by creating a scratch layer and tracing out the outside points (see image below) grouping the points nearest to each other.
However, tracing out the points will take time for me, I tried different methods to generate polygon automatically, but they don't look promising to me.
This is by buffer : rectangular and dissolve. The edges are too sharp and I have to regularly change the "distance" to fit that there will be no holes inside.
This is from cluster, then minimum bounding geometry.