I posted a link to a commentary which tried to explain the mansions. www.craigkeener.com/tag/in-my-fathers-house-are-many-mansions/
“mansions” comes from the Latin translation–it is not in the original Greek text - translating from one language to another can introduce meanings that were not there to start with. The Greek word seems to have meant "dwelling-places" Perhaps the original meant something like "God can dwell in many people and places" - not just in one narrow interpretation. Actual physical mansions don't seem likely.
Craig Keener says -
"In the context of John’s entire Gospel, there is no reason to assume that the “Father’s house” refers to heaven, though it might be an allusion to the Temple (John 2:16) or to the Father’s household (John 8:35; and we are His new temple and His household). More helpfully, Jesus goes on to explain the “dwelling-places”* (NIV: “rooms”) explicitly in the following context. The Greek word for “dwelling-place” used in 14:2 occurs in only one other verse in the New Testament—in this very context, in 14:23, part of Jesus’ continuing explanation of 14:2-4. “The one who loves Me will obey Me, and My Father will love that one and we will come make our ‘dwelling-place’ with that person” (14:23). The related verb appears throughout John 15:1-10: “Dwell [abide]” in Christ, and let Christ “dwell” in you.