What has he done besides write/writing the paper?

What has he done besides write the paper?
What has he done besides writing the paper?

Source: https://www.cpsenglish.com/question/1677

On this web page, the writer says these two sentences are both correct and have the same meaning. But I haven’t found any example of using an infinitive after the preposition “besides” in dictionaries. I’d like to know if what the writer says is correct.

I don't see any difference between the two. I'm no grammarian but I think you are making a mistake by assuming that "writing" is a gerund here. English infinitives come in two forms. The "to" infinitive (to look, to run, to say) and
the -ing infinitive (looking, running, saying).

For example, these two have identical meanings:

1. To look is allowed, not forbidden.
2. Looking is allowed, not forbidden.

probus said:

I think you are making a mistake by assuming that "writing" is a gerund here. English infinitives come in two forms. The "to" infinitive (to look, to run, to say) and the -ing infinitive (looking, running, saying).

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I'm afraid you are mistaken there. The two forms of the infinitive are the bare form write and the to- infinitive to write.

There is no universally-accepted label for the -ing form, but most people recognise the name gerund.

Yes, I agree that both are correct and have the same meaning but I suggest you use the -ing form.