Consider someone talking about how to make a painting of a fish:

We can render (the appearance of the fish) ( in a more realistic style) than was done on this painting to my left, if we apply some silver paint.

With "than was done", the comparand must be the entire verb phrase "render the appearance of the fish in a more realistic style". If we choose a different verb, for example, "than was used" or "than was employed", the comparand becomes "style".

We can render (the appearance of the fish) ( in a more realistic style) than was employed on this painting to my left, if we apply some silver paint.

I personally find the "done" version somewhat awkward, as the semantic focus is on the style chosen to render a realistic appearance, not rendering realistic appearance per se.

Consider someone talking about how to make a painting of a fish:

We can render (the appearance of the fish) ( in a more realistic style) than was done on this painting to my left, if we apply some silver paint.

With "than was done", the comparand must be the entire verb phrase "render the appearance of the fish in a more realistic style". do is semantically anchored to the verb.

If we choose a different verb, for example, "than was used" or "than was employed", the comparand becomes "style". was employed is anchored to what was employed, the style.

We can render (the appearance of the fish) ( in a more realistic style) than was employed on this painting to my left, if we apply some silver paint.

I personally find the "done" version somewhat awkward, as the semantic focus is on the style chosen to render a realistic appearance, not the action of rendering a realistic appearance per se.

Consider someone talking about how to make a painting of a fish:

We can render (the appearance of the fish) ( in a more realistic manner) than was done on this painting to my left, if we apply some silver paint.

With "than was done", the comparand must be the entire verb phrase "render the appearance of the fish in a more realistic manner". If we choose a different verb, for example, "than was used" or "than was employed", the comparand becomes "manner".

We can render (the appearance of the fish) ( in a more realistic manner) than was employed on this painting to my left, if we apply some silver paint.

Consider someone talking about how to make a painting of a fish:

We can render (the appearance of the fish) ( in a more realistic style) than was done on this painting to my left, if we apply some silver paint.

With "than was done", the comparand must be the entire verb phrase "render the appearance of the fish in a more realistic style". If we choose a different verb, for example, "than was used" or "than was employed", the comparand becomes "style".

We can render (the appearance of the fish) ( in a more realistic style) than was employed on this painting to my left, if we apply some silver paint.

I personally find the "done" version somewhat awkward, as the semantic focus is on the style chosen to render a realistic appearance, not rendering realistic appearance per se.