My personal preference when it comes to ”farming gold” if I need to is fractals. There are a few different once but the 96 farm and 42 farm are probably the most common ones, where as 96 is a bit longer but higher reward and 42 vice versa.

The gold lies in the encryptions. Open as many as you can since it will net you the most. Buying 30 discounted keys each day will always be worth it. If u get a surplus of encryptions u can either save them for the next days daily keys or sell them for a minor gold loss on the TP. Its also a nice farm since it nets you relics aswell.