Madmeg. I have a similar professional background, 50 years working in accounting and IT, so my approach to many things is through logic.
I can only speak of my own personal experience in the 20th and 21st centuries.
I have been banking online for about 25 years across a variety of platforms for both domestic and business banking and have rarely encountered any problems. I have money spread across several banks and building societies and find all of the online systems and apps easy to use.
I’ve had an iPhone since they were introduced in 2007 (when I was 52, I’m now 69) and a smart TV since 2020. I find both very easy to use. There was a little bit of admin involved in the set up of the TV, setting up accounts for each app so they can synch across three devices, my TV, laptop and phone, but once done it’s done.
I’ve been a widow all that time so I am used to figuring things out for myself and did anyway when DH was alive. Generally, I’m not fazed by anything new and just take my time to understand how things work. It's part of the job of an analyst/designer/programmer to do so. I read instructions and FAQs and while that sounds obvious, I am aware that a lot of people don’t.
I don’t understand what you mean by not understanding On/Off. The universal symbol for this is a circle broken at the top with a vertical line through it (or sometimes a solid circle with an enclosed vertical line. It’s an amalgam of the binary 0 and 1 - two states - off or on - which your husband should certainly understand as binary logic and binary number systems are what underpins all IT systems.
I’m sitting here with three remote control devices, for the smart TV, for the Humax recorder and the sound bar and all have the same symbol.
Pie charts are a visual representation of fractions or percentages. Some will think a quarter, others will think 25%. I tend to use the terms interchangeably depending on the size of the slice. I’m more likely to say 10% than one-tenth.
Forgetting how to do something really isn’t the fault of the app or the app developer but like learning and doing anything, ease of use comes with confidence and practice.