In the suttas, one finds simple directions such as this:
DN33:2.1.27: A mendicant with defilements ended can’t deliberately take the life of a living creature, take something with the intention to steal, have sex, tell a deliberate lie, or store up goods for their own enjoyment like they did as a lay person.
As you notice, there isn't anything about being a vegetarian or using leather. Those are details. Looking more carefully at the suttas themselves, we see that deliberately taking life is not acceptable. Therefore, if one finds a dead animal in a forest, eats it and makes leather, that is not deliberately taking the life of a living creature.
In modern society, that link between meat and leather is indirect. Others kill so that we may have meat and leather. When we buy meat and leather, we promote such practices, becoming complicit in the killing. Yet now we have oddities such as the Impossible Burger, which does not require the killing of a meat animal.
Not killing introduces us to love and compassion. Indeed, with limitless love and compassion, we simply cannot deliberately kill.
Practicing love and compassion is a start. For example, at the start of AN8.63, we see:
AN8.63:2.2: ‘I will develop the heart’s release by love. I’ll cultivate it, make it my vehicle and my basis, keep it up, consolidate it, and properly implement it.’ That’s how you should train.
Study the suttas and don't get caught up in rules and observances. We have robots for that--they are programmed to mindlessly follow rules. Instead, open your heart to loving kindness and compassion and more. Study the suttas and decide for yourself each moment what Right Action results from Right View. Use the precepts to guide your awareness of what needs to be done moment by moment. This is why the precepts are non-specific. The precepts encourage us to be mindful.