Unless the time-series was only for simple monitoring or querying, I would stay away from key-value databases like Prometheus or InfluxDB which have limited joi

Unless the time-series was only for simple monitoring or querying, I would stay away from key-value databases like Prometheus or InfluxDB which have limited joins and limited analytics capabilities. A fully relational time-series database like Timescale (a plugin db built on Postgres) gives you full SQL analytics, including aggregations and full relational joins with other data, which is where a lot of the value-add usually is. This also opens up the field to building multivariate machine learning models.