Over at varlock (https://varlock.dev -- also free, open source), we agree that .env as we know it is full of problems. But instead of abandoning it, we evolved it. We replace your .env.example with a .env.schema - using decorator style comments to add schema info, and functions to load and compose values.
A big difference between our tool and many other similar tools is that we combine the schema and value setting into one surface, with a way of merging many definitions together, much like cuelang - but in a way that feels more intuitive. It's extremely flexible, and can even do credential brokering for untrusted workloads.
I've been enjoying the secretspec content lately, and watching it evolve :)