Need to upgrade SSD in an additional slot in laptop HP Pavilion 15

Go to crucial website and download their auto upgrade app. Run it in your laptop, it will tell you the best upgrade which required for max performance

For 4TB sata, afaik your choices are limited and really gonna cost you around 25-30K for reliable TLC SSD, for example Samsung 870evo, crucial mx500, adata SU630, etc while QLC SSDs will be cheaper and the go for storage needs where data rewrite is less frequent, the cheaper options include Silicone power, team group, etc. But for 2TB the scene is different there are many options to choose from like WD, Teamgroup, patriot, crucial, etc and the TLC SSDs aren't much costly than QLC SSDs in this range. If budget isn't an issue i will always recommend TLC over QLC for better cell life but if you are only going to store large amount of data without rewriting the data like i do then nothing beats the QLC SSDs value for money.