Hi!
Well, this basically sounds like that the laser died.
I recommend to replace the laser deck, instead of replacing the whole drive. It's cheaper and it should fix it immediately. Fortunately, it's not that difficult for the PS4 Slim!
The part you need: https://www.aliexpress.us/item/3256803704387116.html?src=google&pdp_npi=4%40dis%21EUR%2111.79%2111.79%21%21%21%21%21%40%2112000027398889513%21ppc%21%21%21&src=google&albch=shopping&acnt=494-037-6276&isdl=y&slnk=&plac=&mtctp=&albbt=Google_7_shopping&aff_platform=google&aff_short_key=UneMJZVf&gclsrc=aw.ds&albagn=888888&ds_e_adid=&ds_e_matchtype=&ds_e_device=c&ds_e_network=x&ds_e_product_group_id=&ds_e_product_id=nl1005003890701868&ds_e_product_merchant_id=443046777&ds_e_product_country=NL&ds_e_product_language=nl&ds_e_product_channel=online&ds_e_product_store_id=&ds_url_v=2&albcp=19215243779&albag=&isSmbAutoCall=false&needSmbHouyi=false&gad_source=1&gclid=EAIaIQobChMIpZ6txsDMiQMV3ayDBx1OOzuVEAQYASABEgKtdfD_BwE&gatewayAdapt=glo2usa4itemAdapt (be sure that you have the correct laser deck! Always open it up first to see which version of laser deck is in there! Usually it's the 496, but always check it out first!).
Guide: https://www.youtube.com/watch?v=wxnXStM1sho
Whenever I have some spare time, I will write a guide for it on iFixit.