I identify with this. I'm ready to move on to the next step but there doesn't seem to be a position that fits my experience level. "Senior" seems like a relative distinction based on the company. I'm ready to land at a place that takes engineering practices more seriously but those companies don't think I have enough experience with those practices - for instance, I've never worked at a company that even cares about unit testing, now I need to be very experienced at it. I know how to do unit testing of course but it's not my sharpest skill for obvious reasons. I'm focusing on these weaker skills but it's definitely a challenge.

Same experience. Low level warm-body work is plentiful, but pays poorly and doesn't give good experience. Senior level work is in extremely high demand, but employers aren't willing to bring on engineers who only have experience with the latter. I've started shopping around for (and have had limited success with) 100-500 headcount companies who are willing to hire seniors on the greener side.