This is the problem with the Fixed III SSDs in SATA II Macs like this - they do not work! You need a drive with a SATA II mode, or a Fixed II SSD.
As to what drives I’d recommend there are two:
* [https://eshop.macsales.com/item/OWC/KITIM09HE500/|OWC Mercury Electra 3G (500GB)]
* [https://eshop.macsales.com/item/OWC/KITIM09HE1TB/|OWC Mercury Electra 3G (1TB)]
* [https://www.samsung.com/semiconductor/global.semi.static/Samsung_SSD_860_EVO_Data_Sheet_Rev1.pdf|Samsung 860 EVO]