4 cucumbers displacing ~1cup of water. ~2cup daiso "straight jar"
This is very roughly a "Quick Pickle", suitable for only a couple months. The sort of thing that might last a winter, but can’t contribute to a long-term larder. For longer term pickling, ditching the vinegar and increasing to a 3-5% saltwater brine gets you to roughly 4-6mo. Canning would be the next step up, which requires a supply of lids and canning equipment - but it gets you roughly a year’s worth of shelf-life.
After a week, we found the remaining (non-pickled) cucumbers had large spots of mold on them, meaning we couldn’t use them. This prompted me to check the pickles and realize that the very tips of the cucumbers had breached the solution, and one had a similar mold spot.
This seems to be due to the jar being used - it’s a snap-top, but has an air pocket above the seal. This means that you must be careful to keep anything being pickled well under the top of the solution, even if it initially looks like it’ll fit. Lesson learned; leave lots of head space.
We removed the offending cucumber, lopped almost half of it off (to be sure we got all the mold roots), dumped the solution, and re-jarred.
Too much vinegar. More salt and mixture of other vegetables in the brine (garlic probably) is going to be required. These became acidic and sour. While completely edible, they aren’t the right flavor. They’re more an "ingredient" to go along with meats and dumplings, rather than something you could crunch on alone.