Not sure how correct I am but the assets available you can add sort of answers the questions so if you can add USDT to fx core wallets and pundi x chain wallets, Polygon wallets and tron wallets, then I would gather you can crosschain or bridge USDT between them, as there is no BNB wallets to add for FX core or Pundi x chain then BNB at this time it’s restricted to the BSC wallets of the fx wallet app.
question is what do you need on polygon and tron chain wallets for fee’s or are they in fx i assume being a fx core wallet app tx, unless your going out of pundi x chain it would be a Pundix fee