via [PostgreSQL and UUID as primary key](https://maciejwalkowiak.com/blog/postgres-uuid-primary-key/) i stumbled upon [TSID Generator](https://github.com/vladmihalcea/hypersistence-tsid), which looks interesting:
> A Java library for generating Time-Sorted Unique Identifiers (TSID).
> ...
> In summary:
>
> * Sorted by generation time;
> * It can be stored as an integer of 64 bits;
> * It can be stored as a string of 13 chars;
> * String format is encoded to Crockford's base32;
> * String format is URL safe, is case insensitive, and has no hyphens;
> * Shorter than UUID, ULID and KSUID.
also, from the comments: https://sqids.org/
> Sqids is a small open-source library that can produce short, unique, random-looking IDs from numbers.
> The best way to think about it is like a decimal-to-hexadecimal converter, but with a few extra features.
>
> What is it good for?
>
> Link shortening, generating unique event IDs for logging, generating IDs for products/objects on a website (like YouTube does for videos), generating short IDs for text messages, confirmation codes in emails, etc.