We have a list of the supported Luxembourg Payment Gateways here. The good news is that there are quite a few to choose from!
I don’t have details on each gateway’s terms of service, but I recommend deciding on the top 3-5 that you’d prefer to work with and then checking out their websites or reaching out to their support teams to see if they support dropshipping.
In the meantime, I have submitted feedback to the team to let them know you’d like to see Shopify Payments available in Luxembourg. Updates regarding Shopify Payments availability will be posted on the Shopify Changelog.