(Microsoft) Forecasting best practices: https://microsoft.github.io/forecasting/
(Harvard) Unified time series model: https://github.com/mims-harvard/UniTS/tree/main that can process various tasks across multiple domains with shared parameters and does not have any task-specific modules.
M forecasting competition: https://forecasters.org/resources/time-series-data/ The data is freely available for anyone to use and the data can be used by any researcher without further permission.
DL time series model library: https://github.com/thuml/Time-Series-Library an open-source library for deep learning researchers, especially for deep time series analysis.