Well, I went to my branch on Tuesday to get mine sorted out. It seems I opened the Krungsri app on my old phone, (in 2020, although I never remember doing so, or ever using it*), and didn't delete it, so when I tried to open it on my new(ish) phone it stated I already had the app, even tough it never showed in my apps list. Anyway, now sorted. So I have the Krungsri app, plus I have a Krungsri Biz app (for a joint account), so I couldn't add the sole account to that. *I'm only a spring chicken 68 year old, although memory seems to be a failing; what happens after I turn 70 is anyone's guess.
The only issue I have with the Krungsri app is I cannot read a transaction list for say 6-12 months, (as is possible with online banking). Maybe something I haven't yet mastered, and reluctant to eff around with it, as apart from anything else, it has my IMM 800K dosh in it, which I don't want affected.
You will be able to use the Biz app even after 70, despite their blurb and what they say. My partner is 71 and it worked perfectly; others too have reported successful opening of Biz app even though they are 70+.