Is it prohibited to bring or check in more than 80ml of undiluted solution on domestic and international flights? Since undiluted liquids don't contain LPG (high-pressure gas), I assume they're allowed. What do you think?

Liquids are generally restricted in carry-on baggage by many airlines.
On the other hand, it is believed that in many cases, liquids less than 100 ml are allowed to be included in checked luggage (suitcases, etc.), as are cosmetics and detergents.
However, the specific regulations of the airline you are traveling with may vary, so we recommend that you contact the airline in advance to be sure.