To be honest, Goodbudget isn’t really meant to track assets that aren’t strictly monetary and aren’t used in normal budgeting. If you really wanted to track the value of your assets over time in Goodbudget, the best methods would be either this workaround for tracking off-budget savings accounts, or this other workaround leveraging the Debt Account feature backwards. Both of those would require you to manually update the values once in a while, but would allow you to use Goodbudget to have a more total holistic view of your assets.
…if you’re asking how to create a balance sheet in general, outside of Goodbudget, then I’m afraid that’s above my paygrade, but maybe someone else will be have some knowledge about that.