Many banks do this now. Chase, Monzo, etc. force you to use their mobile app to not just do money stuff but view statements. At least they have the ability to 'share' the documents so you can email them to your PC.
The one you show, XLN, at least give you the option to still view online (presumably that's what the "you can still access all of the invoices here" thing is). Bear in mind that the trend is for people to use mobiles to do things nowadays, 1 so a mobile app is better than trying to use a web page, or to download a pdf that you don't have a viewer for. In that context it's just catering for modern users, but old farts like us can still view online if we want .
For a bank with money transfers but for an ISP that does not involve money transfers and so on I find that plain stupid.
Joke:
1 I find a desktop browser with controls on it so much better and easy than using a "mobile app" with a keyboard that hogs screen space that I can imagine maybe possibly littered with fixed headers and widgets, animations; fake loading spinners, animated skeleton placeholders and dimming overlays that cut me off from the contents whatever is left (with the dimming hurting my eyes) and no adblock to kill them like with a browser.
Actually you might know the ones that do the above annoyances if you use them. I am hoping they'd stop that nonsense one day with the above.
The other more and more prevalent (near) forced use of mobiles is for MFA.
Banks for example will very often now ask you to sign in on your mobile as a way of authenticating for online or phone transactions. The mobile platforms are actually considerably more secure than the average home desktop. Surprisingly Android and IOS provide enough layers of sandboxing and SSL lockins that banks et. al. actually trust mobile environments more than a desktop.
I am not happy about having the banking presence and access to my account on a phone that I take everywhere that I only use to make calls. I'd feel the need to buy a phone just for that to separate it. Also the wifi portion too (my paranoia) but maybe I could buy a ethernet adapter.
I had an idea that maybe the bank could issue modified phones or devices just for the purposes of banking, that are kept at home for customers but with the annoyances I find above I think I'll go into the branch whatever one is left and the paper invoices which is not ideal but I think I prefer that whilst they are still going and I see they may not be there pretty shortly.
So if, I have a probem with the "smart phone", won't turn on, wifi issues, no longer supported etc, that means I won't be able to view stuff.
The ONE and ONLY way of just viewing stuff which I find VERY STUPID.
I think they should stick to both mobile and desktop browser (with some authentication) as a backup and for convenience.