Since 1 January 2021, the transition period for the application of the Registered Exporter system (the REX system) in the Generalized System of Preferences (GSP) is over for all countries.
Then, since that date, the REX system is the only system applicable to certify the origin of goods in the GSP, and the competent authorities in the GSP beneficiary countries may not issue certificates of origin Form A anymore.
The competent authorities in the GSP beneficiary countries may of course still continue registering exporters.
A certificate of origin Form A which has been issued in a GSP beneficiary country during the transition period, and which is still in its validity period, is still admissible in the EU to claim the benefit of the GSP. For the dates concerning the transition period for all GSP beneficiary countries, you may look here.