You appear to have a fundamental misconception as to what an analogy is and what it isn’t, where and when to use an analogy, and so on.
An analogy is where, for the purposes of explanation, you highlight an area of similarity - typically singular - between two often abstract matters. An analogy doesn’t have to be a full, factual comparison between the two matters, and neither does it imply a full equivalence between the two.
Henry Kissinger once made an analogy about bringing troops home from Vietnam and eating salted peanuts. Two very different matters. Forrest Gump did the same about life and a box of chocolates. I don’t think even Forrest Gump would believe that life is actually fully equivalent to a box of chocolates, and on the same basis there’s no reason to believe that someone making an analogy between Brexit and the Y2K bug implies that they see the two matters as fully equivalent.
The issue here is that Brexit has forced companies to spend sometimes millions individually - and billions collectively - in order to mitigate the impact of an event on their operations, and help ensure that they can continue to operate in their chosen markets. Financial services companies have in some cases set up subsidiaries in the EU, manufacturers may have to shift production capacity, importers will now have to hold higher stock levels and employ more people to deal with customs declarations. All well documented consequences of Brexit.
The analogy relates to the fact that this expenditure is from an economics perspective a sunk cost, in that it’s necessary to continue to operate in or enter a market, but it doesn’t actually boost the company’s productive potential. And of course there’s an opportunity cost to this expenditure, another basic concept. So the analogy with the Y2K bug is obviously valid - Y2K expenditure was actually a very good example of a sunk cost - even if this expenditure will continue for Brexit where it didn’t for Y2K.
Now I would hope that if Forrest Gump can properly understand the concept of an analogy, then you should be able to as well. Although I have to say that this confidence doesn’t extend to all the posters on this thread.