Many people appear here and all over the internet are of the opinion once someone opens your phone that isnt apple and replaces the screen, for instance, apple suddenly loses all responsibility for any faliure of the device whether or not it was related to the repair due there being another possible person who could have created the issue and by vertue apple is immune to any repicussions related to the faliure of the device even if apple caused it. This is the last person to touch it is the only one who can be at fault rule i suppose. The australian consumer law might be interesting to you because it was set up and backed up by cases before apple started to try moving goal posts.
The basics of it are:
-If you say you do something and it doesnt happen, make it happen or in trouble (time frames, what is and isnt reasonable then come into play).
-for the lifetime (resonable appears again, 10 year old iphone vs 1 year old iphone kind of logic applies when thinking resonable not 23 vs 24 months) of the product the company is responsible if a faliure arises due to resonable use (so putting phone in pocket alot cause touch disease is apples fault but dropping phone on concrete isnt).
This is where i guess it will be weird for those with the "the last person to touch it is the only one who can be at fault rule" position as these apply to all parties in the original post scenario, apple and the repair shop and all of this appears logical when focusing on an individual phone
Person buys iphone, person drops iphone, iphone is broken but since the person broke it in an unresonable use of the phone (hitting ground at high velocity), person is responsible for repair and gets it repaired,(ACL makes it very clear who repairs it doesnt matter because if something is broken due to faulty repairs because they advertise "make phone work" if they give phone back that dont work it's their problem not apple), phone works again, apple release update, apple update breaks phone, apple responsiblity is verified, apple in deep shit because something purchased called an iphone doesnt iphone and it was apple's fault.
The Australian make sure everyone plays nice website goes into more details and with less iphone related examples.
https://www.accc.gov.au/consumers/consumer-rights-guarantees/repair-replace-refund?gclid=CjwKCAjw06LZBRBNEiwA2vgMVZBAJjGmNt1uE1gUj1LGvzo384-eUfKcCF29MTWwt7OKZLlxL09pyBoCtU0QAvD_BwE