Again: I don't think this is a mainstream Catholic church thing. You'll see downthread people besides myself relating stories of priests consecrating Triscuits or wine parishioners brought back from trips. Eastern-Rite Catholics all use leavened bread, apparently.

Traditionalist Catholicism (tradcath-ism) is not the same religion as Roman Catholicism. It's a weird splinter thing.

Why would what’s true and required about the Eucharist (at the most fundamental level) change from, say, 1923 to 2023?

The matter at hand is not a trad thing (but I will disclose that I am in the trad camp): these are just basics covered in e.g. the 1997 Catechism promulgated by John Paul II and the the 1983 Code of Canon Law, which are 100% mainstream.

Traditionalist catholics celebrate the mass as it always was. The new religion you are alluding to that would consecrate a triscuit is what is out of lines. You can't accuse a group that stays the same as creating a new religion while you consecrate snacks from the grocery store.

Nevertheless, there is no objection to using eastern rite leavening or wine made from grapes from elsewhere. The eastern rites are just doing what they've always done and the wine just has to be grape wine and fermented. This is not a novel rule. It's how it's always been done. You can read any older document on the matter to realize the so called traditionalists are not creating a new religion.

That's fine! Every religion has an intricate set of justifications for its practices and I generally respect them all. All I have to say about traditionalist Catholics is that they aren't mainstream Catholics.

This is like calling protestants mainstream Catholics because there are more aggregate protestants in the us than Catholics. At some point we must be clear as to definitions. If you start doing things like consecrating triscuits you are not Catholic. You can be whatever you like but it is simply dishonest to say you're Catholic. Anymore than the protestants are.

Wine is fermented grapes?

The argument is not that the definition of wine is malleable (which it definitely can be without falling down your slippery slope), but that being picky about the definition misses the point of the Eucharist entirely.

Well, when Jesus was incarnated on Earth his primary focus was on how we just have to be loose with our definition of wine.

I don't know why the Catholics have such a problem with this. Pretty much every story you read about Jesus, he was pointing out how wine could be anything. Even water.

So yeh, being picky about the definition of wine is probably the most blasphemous thing anyone could say or do.

If you tried to sell a bottle of milk as wine, you’d get in trouble fast.