though one thing to note about singpass is that as of now, it's not 100% given that singpass will 100% work on local set at this point in time, since no one has local set? unless got some ppl testing it here already. or unless there are folks using those official global units from other countries that can chip in? if google a bit, not hard to find precedent about singpass having login issues, even on phones sold officially in SG.
This one can only wait to see if govtech will fix the app or not, and i think it's something that will probably be fixed eventually? i had the same login error on redmi k70 pro on CN HyperOS a few weeks back, but then last week was able to login suddenly albeit with some error still (some signing certificate error, but doesn't affect logging in to gov e-services at least). ¯\_(ツ)_/¯