Luxembourgish is a very small language. Resources lack a bit. Below a short list.
Learn Luxembourgish with Anne - an online self-paced course (and not too expensive). Anne is very responsive, answers questions within a short time. You log in to the website and download the videos with explanatory pdf files. Anne covers basic topics with ample explanations, you have lifetime access. If you make your homework after each lesson and send it to her, she corrects everything and you get a discount for level 2. Worth every penny! A good resource to get a kickstart in Luxembourgish.
Luxembourgeois à grande vitesse, Assimil - a good resource (not that there is much choice), although I find that it is tailored to people planning to move to the country. The vocabulary is not always as interesting if you are learning the language for other reasons than a move. I like the grammar explanations.
Websites - there are a few websites and Twitter accounts where you can find reading and listening material: eldo.lu, moien.lu, 100komma7.lu.
ZLS - Zenter fir d'Lëtzebuergesch Sprooch - they publish books, novels, vocabulary builders (d'Lëtzebuerger Verben, Aläert ...).
Netflix - 1 series, only 1, but worth to watch! Capitani (a second series is announced).
Italki - of course! I like conversation practice and Melanie is one of the best teachers.
Schwätzt dir Lëtzebuergesch B1 - published by ZLS. A regular textbook, with grammar and loads of vocabulary. I know they also have the A-series, so if you are planning to study Luxembourgish, go and have a look at their website.
Reading - there are more and more books published in Luxembourgish, I bought Pipi Longstocking in LUX and use this for reading practice.