You know the old chestnut, one of the enduring allures of alternate history fiction as a genre: “Hey, what if the Roman Empire survived ?”, “Hey, what if the Incan Empire survived ?”, “Hey, what if Anglo-Saxon England never had any Norman influence after 1066 ?”, “Hey, what if the Byzantines survived 1453 ?”, “Hey, what if France or China were still monarchies ?”, and so on.
More often that not, overly casual or amateur/inexperienced writers of alternate history works seem to assume that if some OTL country or culture that ceased to exist at an earlier point in history survives in an ATL, the basics of their culture, clothing, attitudes, language, etc., will forever remain static and largelly unchanging. Worse yet, many such authors assume that the best way to show it is to have these surviving cultures from older periods wear stereotypical clothing associated with the culture, use stereotypical architectural styles associated with the culture, and have stereotypical customs and behaviour associated with both facts and clichés about their culture. All of this well into the Space Age, even if the divergence occured in the Bronze Age or whenever.
Also called the “Civilization effect” or “Alternate History as a Computer Game Effect”.
There's also a more insidious side to the whole thing: Assuming that just because cultures like the modern day Maya or Aztecs no longer live and behave like their ancestors in the 7th century or 15th century, that they are “no longer real Maya and Aztecs”, or even worse, that “Maya and Aztecs existed once, but don't exist today”. Several millions people of Maya nationality and Aztec (Mexica) nationality in modern day central American countries would beg to differ. This is like claiming that just because people from modern England do not live “like Anglo-Saxons in the early Middle Ages, just with modern technology”, there is no historical continuity between the two. Of course, this ere is a clear continuity
The key feature of this cliché is assuming that there's one blanket stereotype for everything that defines a historical or contemporary nation/culture/country, and anything deviating from that stereotype is “incorrect”. This is a very simplistic view of history, as the entirety of real human history is about very complex processes. Each human culture throughout history has undergone complex developments and changed over time, often in complex and unrecognisable ways. If we understand that someone from medieval Switzerland or China would not be the same sort of individual from modern day Switzerland and China, becuase the countries and their cultures have developed and changed greatly in just five hundred years, then it's safe to assume a “surviving modern Rome” wouldn't have riot police engaging protesters with kevlar scutum shields and rubber gladii (as cool as that would no doubt look). History is complex, changes and developments in individual cultures are complex, and no culture can be boiled down to just one neat, simplistic stereotype that will never change in an alternate timeline.
1.) Doing your research - not relying on popular but often completely inaccurate stereotypes and shorthands.
2.) Respecting causality - thinking logically about the repercussions of your changed historical events and paying attention to the butterfly effect.
3.) Keeping the outcomes reasonable but original - an alternate version of a culture, including a surviving one, might have features unusual from an OTL point of view, but reasonably, logically established ones, instead of predictable visual clichés or other lazy stereotypes.
No, if Ancient Egypt - really, which ancient Egypt ? Old Kingdom ? New Kingdom ? Ptolemaic ? - never fell and continued to the present day, it's doubtful people would still be building pyramids or tombs in the Valley of Kings with slave labour, all the while using smartphones, riding around in electric cars, holding democratic elections, and wearing casual sportswear with a few token ancient Egyptian stylings. If an ancient Egyptian society survived to the present day, it would likely still evolve in ways as to be eventually uncrecognizable to what it was like 2000 or 3000 years ago. Various new nations and powers and religions, as well as commercial changes and technological advances, will pose challenges to a surviving ancient Egypt, as preserving its “stereotypical” nature straight out of antiquity will not help it as a country surrounded by continuously advancing neighbours. Egyptians are unlikely to be flying into space, while still using horse-drawn chariots and bows in battle, rather than tanks and rifles. It is likely that if there was a more direct continuity in the alternate timeline, it is still likely the resulting Egypt would be closer to modern day Egypt in timeline, in terms of society, tech, culture, religion, economy, not closer to what ancient Egypt was like 2000 years ago.
Butterfly effect - Scenarios with this level of stereotyping often disregard even the basics of the butterfly effect (causality) completely.
Citroen DS Incident - When something in a fictional or alternate culture references the real world to such an extent that it strains credulity.
Wank - The tendency for black-and-white thinking in storytelling and worldbuilding, having everything or nearly everything go well for a particular historical culture, nation or group, all the while coupled with heaping nothing but endless misfortune and misery on other cultures (especially the supposed “rivals” of the “favourite” culture).