I guess I should elaborate on that. Pseudepigraphy was very common during the intertestamental period, and before then as well. This was a time when modern established notions of authorship and textual finality did not yet exist. That a “valid” text is one that is: created over a single, not-too-lengthy time period; has a single final form; is the product of a single attributed author (or if multiple contributors, then all are credited); and that anything otherwise is an offense of some kind (plagiarism, forgery, etc) - these notions did not yet exist. Think about the production of the Pentateuch, by redaction in committee as it were, a few hundred years before the creation of today’s Daniel - or think about the prophetic books which are commonly acknowledged as being collections of oracles (some written, some spoken) by disciples, potentially over generations, some of which oracles came from the original prophet and others which came from disciples later - and you can see other examples of this all throughout the conclusions of OT scholarship. Daniel is not much different.
When we use the word “forgery” it brings along connotations of nefarious intent - an intent to deceive for purposes of self-aggrandizement or profit, for example - precisely because, in our age and culture, we do have such strong notions of textual finality, integrity and authorship. But back in the day, in the ANE and intertestamental periods, they didn’t, and the evidence of that is in how commonplace and unremarked-upon pseudepigraphy was (and other violations of modern textual norms, such as anonyomous redaction of pre-existing content, or insertion of new content). So, that’s why I don’t see Daniel’s pseudepigraphical nature as a huge strike against it; like with much of the rest of the Bible, this is simply another exhibit of its “enculturated” nature.