can you use pre-paid cards on stores like humble or fanatical

I used this site in the past with no issues. Not sure if it has exactly what you need though
https://www.cryptorefills.com/

Humble won't let me but I use a debit card on Fanatical without any problems.

I have used pre-paid cards with both Humble and Fanatical, though at least humble doesn't accept all of them.
Not sure about the card you linked. It should still be usable at other online stores most probably.

new question - would i be able to link the card to my paypal account - as i found this - https://www.businessinsider.com/guides/tech/how-to-add-gift-card-to-paypal?r=US&IR=T

I have used prepaid mastercard with humble bundle. It did not work everytime. Sometimes they let me use the prepaid cards for the choice subscriptions, other times they declined it saying humble subscriptions does not allow prepaid cards.

And yes, the prepaid mastercard I used, I was able to link it to paypal.

i've also thought about going the selling route though a site like this - https://paxful.com/sell-bitcoin/paypal to turn it into paypal then i would have little problem spending it

I believe the IndieGala store accepts crypto. They used to constantly have sales where paying with crypto would give you a discount. (Not sure if they still do, but only because I'm not following sales on any store very closely any more.)