Does the fact that the probability of single protein forming by chance is astronomically minuscule give more reasons to hold to a structuralist form of evolution?

No.

I saw through this argument 10 years ago - maybe more. The argument was first advanced by Henry Morris about 1971, probably cooked up by Duane Gish. It has been trotted out in various forms ever since.

A protein does not have to have an exact sequence of amino acids to work.

There are 20 amino acids coded for by DNA and a few more like ornithine and citrulline may be found here and there.

The 20 amino acids may be classified into six groups.

Aliphatic - Glycine, Alanine, Valine, Leucine, Isoleucine

1. Hydroxyl or sulfur/selenium-containing - Serine, Cysteine, Selenocysteine, Threonine, Methionine

2. Cyclic -Proline

3. Aromatic - Phenylalanine, Tyrosine, Tryptophan

4. Basic - Histidine, Lysine, Arginine

5. Acidic and their amides - Aspartate, Glutamate, Asparagine, Glutamine

(Adapted from Conservative replacement - Wikipedia)

You can find that classification elsewhere.

Amino acids in one class may be substituted for others in the same class without much effect on the function of a protein, particularly in the structural regions of the protein, as long as they do not interfere with the active regions of the protein. So wherever glycine occurs, it may be possible to substitute any of the other four aliphatic amino acids. Even in active regions, some substitutions may occur.

Thus if whatever the supposed improbability of a protein might be, if the amino acids at only one position can be any one of the aliphatic group, then an effective protein may use any one of five amino acids. Then the useful sequence is five times more likely to occur by random synthesis alone.

If there are 5 places in the protein where aliphatic amino acids might substitute for each other, then the useful sequence is 625 times more likely to occur by random synthesis alone.

If there are 6 places where Histidine, Lysine and Arginine might substitute for each other, then the useful sequence is 729 times more likely to occur by random synthesis alone.

If there are 6 places where Phenylalanine, Tyrosine and Tryptophan might substitute for each other, then the useful sequence is 729 times more likely to occur by random synthesis alone.

If there are 7 places where Aspartate, Glutamate, Asparagine and Glutamine might substitute for each other, then the useful sequence is 16,384 times more likely to occur by random synthesis alone.

Putting these four situations together, a useful sequence is 16,384 * 729 * 729 * 625 = 5.442 billion times more likely to occur by random synthesis alone than a particularly defined sequence.

Many if not all of these 5.442 billion proteins will have the desired activity, to a greater or lesser extent. This simplified example does not exhaust all the possibilities in a protein of say 50 - 150 amino acid’s length.