In short...no. Other than Rovers and Rangers which are generally not sold online, and obscure stuff like SailRail.
Irish SailRail is quite widely available online, the Trainline app handles it easily enough.
I suspect you'd have more issues at a ticket office than online these days. I'd like to see the reaction from a London Overground or Merseyrail station!
Netherlands SailRail is handled by the Stena Line website.
IOM works when there is availability.
A significant number of the most common ranger and rover tickets are now online.
Plusbus online.
London / International CIV online.
Sleepers online.
Staff Travel online (mandatory in some cases)
Railcards all major ones online - some regional ones are now online like Devon and Cornwall. Rest to follow.
If anything, a ticket office can be more expensive as certain tickets are no longer able to be retailed by them, and are wholly online or TVM only, such as some Advance fares or promotions.
Other than excess fares, platform tickets and very odd/rare supplements, you'd at least want to compare prices online before using a ticket office.