Since recent news like bank app only need Android/IOS no SMS TAC or whatapps are not supported. For some people, they just really need basic phone, sometimes only want whatapps.

Yes.. and Huawei, has it's own appgallery but the OS is also Android.

Do not install anything other than WhatsApp and uninstall any others app that you do not need.

I do not see a problem here.

Banking apps could be a slight problem but you could just not use online banking entirely

But for whatsapp, there's actually a 3rd decently popular os for dumbphones these days, KaiOS

Got Facebook, Whatsapp, Youtube, Maps, etc, the basic apps

So that is an option if you just need those
(of course dont expect a great experience watching youtube on said phone)

Without a phone for secure apps, can I still proceed with fund transfers, pay bills, reloads hp by inputting the favourite billers/account via ATM and later use the web online banking whereby since it's been favourited, they will allow any fund transfer without further verify via apps? And of course Limits to be set at ATM as well I assumed Limits also discontinued from SMS Tac authentication.