I bought this one, it was priced good and is also a top pick for most reviewers.
I have a 64GB version not the 512GB. And the protector was the Involer screen protectors:ivoler 3 Pieces Screen Protector for Valve Steam Deck, Premium Tempered Glass Glass, 9H Hardness, Anti-scratch, Bubble Free https://www.amazon.co.uk/dp/B09CKPX9H1/ref=cm_sw_r_apan_glt_i_FHWN2HKA341XFB8CXZ9E?_encoding=UTF8&psc=1
https://www.amazon.com/gp/product/B09CKPX9H1/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 got this for the screen protector shortly before I sent that message. https://www.amazon.com/dp/B09B1J3BK2?psc=1&ref=ppx_yo2ov_dt_b_product_details this is the SD card I picked if you care.
[3-Pack] Screen Protector... https://www.amazon.com/dp/B09CKPX9H1?ref=ppx_pop_mob_ap_share
I've been very pleased with them!
https://www.amazon.com/gp/product/B09CKPX9H1/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
I use this one, it doesn't fit over the entire screen though... good part is it went on super easy and you can't even tell it's on. there's probably a millimeter of clearance on each side.
I bought these: https://smile.amazon.de/gp/product/B09CKPX9H1
They are a perfect fit BUT: 2 of 3 Protectors were broken so I only had one try. And the touchscreen still works but you have to press way harder to register a press
[3-Pack] Screen Protector... https://www.amazon.com/dp/B09CKPX9H1?ref=ppx_pop_mob_ap_share