grammaticality - What is the grammatical function of "which" in this sentence?

I am trying to understand various instances in Hansard, the documentation of proceedings in the UK parliament, wherein the word which is used in an unusual (by my modern parlance, at least) position, one assumes in a formal manner.

An example arises in the choice of words used to introduce a Commission in the House of Lords to facilitate the approbation of a Speaker of the House of Commons. Here is an example from 1905 - with obvious modifications to gender pronouns for referring to the monarch and female members of the houses, similar examples can be found to the present day:

My Lords and Gentlemen of the House of Commons, it not being convenient for His Majesty to be present at this time, a Commission has been issued under the Great Seal, commanding us and several other Lords to notify and declare His Majesty's approbation of the choice of his faithful Commons of Mr. James William Lowther to be Speaker, which Commission you shall now hear read.

(Emphasis my own.)

What is the grammatical role of the word which in the final clause "which Commission you shall now hear read"?

One assumes it is acting as a pronoun to the word "Commission". However, this sentence construction feels quite jarring to my modern interpretation, where I most commonly encounter "which" used to introduce a relative clause, typically without further mention of the referent.

What is this construction and is it applicable in modern written English? Is it a less common use of a relative clause? Is it only there to clarify the antecedent, given the complex nature of the preceding clauses may make this non-obvious?

Without knowing very much about the grammatical specifics in this case, does the sentence below, for example, make any sense?

I believe it uses X, which technology is officially no longer supported.

Answer

... commanding us and several other Lords to notify and declare His
Majesty's approbation of the choice of his faithful Commons of Mr.
James William Lowther to be Speaker, [which Commission you shall now
hear read].

Here, "which" belongs to the category (part of speech) determinative, and its function is that of determiner in the noun phrase "which Commission", serving as object of "hear".

Such use of fronted NPs like "which Commission" is rare, probably archaic: it would be more usual for the NP to be complement of a preposition, e.g. "of which Commission".