Does converting money from dollars to dinars through an electronic platform, with a delay in its arrival to the bank account, entail Riba An-Nasi'ah (usury of delay), or is it considered constructive possession that permits the delay? And can this process be construed as an agency rather than an exchange?

There is no objection to the questioner's dealing with the (Upwork) platform, which undertakes to convert dollars into dinars and transfer them to him, because the exchange transaction does not take place directly between the questioner and the platform, but rather between the platform and the entity from which it exchanges. The platform must observe the rulings of exchange and actual or constructive possession.