Gromit's post seems to working from a false premise anyway. There is absolutely NOTHING in the government's guidance to the hospitality industry which say that pub must use apps.
The guidance simply lays down basic principles and it's up to individual licensees (or the company's that own the pubs they work in) to determine the best ways to ensure that the guidelines are complied with:
https://www.gov.uk/guidance/working-safely-during-coronavirus-covid-19/restaurants-offering-takeaway-or-delivery
So, while some pub chains and/or individual pubs might choose to go down the route of requiring customers to use apps, others can make the use of apps optional or simply not have them at all.
The requirement is to ensure that the guidelines are followed, not to follow them in any particular way.