I believe that Basel Accords are not directly imposed on banks. Instead they are global recommendations. But in practice, all national financial regulators (e.g. FCA in UK) adopt Basel guidelines as minimum standards. Regulation does change across borders since national regulators can impose stricter or different rules to Basel. Also areas that are not covered by Basel might still have regulations, e.g. VCTs are special tax investment vehicles in UK covered by specific rules. ETFs will have rules put in place by the national regulator, and by the exchange trading them too.
As a financial security or risk exposure they will be subject to some form of capital requirement and liquidity requirements as per any other bank asset/liability.
If you go here: bis.org/bcbs/basel3/compilation.htm, and look at 14 Jan 2016, if you look here bis.org/bcbs/publ/d457_inbrief.pdf it says there is a revised market standard in Jan 2019. But anyway this is just capital requirements for market risk, there will possibly be other capital requirements