That’s the thing about functional harmony; because it’s so closely tied to the major scale (and especially its historical use in European classical music), it sort of starts to fall apart the further you drift away from it. That said, it still kind of works in minor, but the “rules” are both different and less clearly defined.
Starting with the ii° chord, if anything it actually works better in minor than in major (at least imo): because the tonic is a darker sound, resolving to it from a diminished chord isn’t quite as jarring. Extending the ii° to a 7th chord gives you ii7b5, whose first inversion is iv6, which also resolves pretty well to i.
I bring this up because the standard iv and v chords in minor are in a sense, reversed from their major counterparts. The v chord doesn’t resolve to i nearly as well as in major because its third (i.e. the 7th degree of the scale) is a whole step away from the i chord’s root (rather than a half step away as in major’s V-I), so it presents a dark, almost melancholy feel (functionally, it would act as a subdominant chord). However, the iv’s third (the scale’s 6th degree) is a half step away from the i chord’s fifth, so it sort of acts as a minor leading tone, in a sense making it a dominant chord. Kind of.
If you were to use major IV and V in minor, you would be borrowing them from other scales: IV is used in dorian, which is like minor but uses a natural 6 instead of a b6 for a more relaxed sound, while V is borrowed from major, or more often harmonic minor, which is minor with a natural 7 to reclaim major’s leading tone (although this results in an unusually wide gap between the 6th and 7th degrees; this isn’t necessarily a problem, but just something to keep in mind).
Going back to functional harmony, most chords besides the i and borrowed V can act as subdominant chords. VII can be subdominant or dominant (since you’re basically using the V from the relative major), while VI can be tonic (since it’s a third away from i and thus only differs from it by one note) or subdominant (again, by serving as the relative major’s IV). Even the minor iv can act as a subdominant.
The III is basically just tonic, but because it’s also the root of the relative major scale, you have to be careful: if you sit on the III for too long, it will just sound like you’re playing in major. It’s best used in short bursts (unless you’re intentionally trying to be ambiguous, which is absolutely a valid option).
In terms of other secondary chords, you’re certainly welcome to use secondary dominants, serving more or less the same purpose they would in major (or any key, really). Sometimes you’ll see the bII borrowed from phrygian, especially in its first inversion (N6) as a subdominant leadup to V.
Hope that helps!