As Today's Plan is shutting down per March '24 and I suspect many coaches and athletes will want to migrate to Trainingpeaks. Me and my coach have been using Today's Plan for years and I have been using it as the single source of truth for running, cycling, sleep and wellness metrics.

As API access to Trainingpeaks isn't available to single users, there's not really a simple way to upload historical data. Please upvote if you're up for some kind of solution (thinking out loud: provision of a CSV template by Trainingpeaks with mappings from Today's Plan data export function and import functionality of other data than activity files, full fledged synchronizing capability).

I'm happy to provide more formats, data types, docs, ideas and devote time to this. I've included a screenshot of the types of data dumps Today's plan allows for from their UI.