/usr/lib/unifi/data/system.properties

unifi.https.ciphers=ECDHE-ECDSA-AES256-GCM-SHA384,ECDHE-RSA-AES128-GCM-SHA256
unifi.https.sslEnabledProtocols=TLSv1.3,TLSv1.2

sudo systemctl restart unifi