Sick fig tree, what can be done?
I have two trees, they may be different varieties. Although both produce large dark purple figs, the inside of the two trees' figs are different. One is juicy & colored as expected, while the other is very dry inside & much whiter. Both trees get plenty of water, though not in excess (However, it is possible that the sick fig tree has received more water). The dry tree has rarely ever given healthy fruit. I've had both trees for years though the one that gives dry fruit grew on its own.
You say the not-so-good tree grew on its own? Volunteer fruit trees that grow from seed usually produce fruit of inferior quality because quality fruit often does not breed true. The tasty fruit tree has been cultivated for years, and possibly grafted onto sturdier root stock. If you want another fig that bears nice fruit, your best bet is to plant a new tree. This article has some ideas: https://www.gardeningknowhow.com/edible/fruits/figs/different-types-of-fig-trees.htm