Yes that is the question, do capital gains have to be reported as part of the AMT calculation? It was quoted as such in the 2014 pdf I mentioned, and also in this 2010 slideshow: https://eiger.law/wp-content/uploads/2016/10/2010-BCCT-AMT-Taiwan-Tax.pdf
I assumed this was no long valid as the new tax on capital gains from securities trading was abolished in 2016, but then I found out that’s a whole different tax.
On this page from 2019 someone replies that foreign investments like ETFs and bonds should be included in AMT, but they don’t mention the exact law: https://www.foreignersintaiwan.com/blog-370963385326684/income-tax-filing-for-expatriates-in-taiwan
I got confused because older documents explicitly mention securities trading to be included in AMT calculations, but newer ones do not. I guess that’s because the tax on local securities trading got abolished (it was explicitly meant to boost the Taiwanese stock market), but foreign sourced trading is still included as foreign income.
From what I can tell, Taiwan does not tax capital gains on locally traded public/over the counter securities*, but anything traded outside of Taiwan can get taxed under AMT as foreign income.
Note * It was reported last week that capital gains from non-public shares and certificates trading will be taxed as income starting next year, because it seems people have been using those as a vehicle to avoid tax on real estate sales.