There is a new section in Control Panels > Trackers > 'System Trackers' (bottom of the page) in Tiki23.
The first one available is the Exchange rates tracker.
You can enable it, select which one it is, select the corresponding fields (Currency, Rate, Date) and also the conversion logic (if the rates are entered straight or reverse pairs). An important update here is removal of the Currency Tracker selection in the Currency field options. We no longer need or want to use that from the field properties as we have a system tracker now. The important part for those of you managing Currency fields is to go to Trackers settings page and configure the system tracker fields.