The Instituto Cervantes is a non-profit Spanish organization developed by the Spanish government to promote the study of Spanish language and Culture.
On their website, you can find self-guided courses for levels A1 to C1. Sixteen 30-hour courses cover 48 topics, each with videos, reading material, and interactive exercises. There is a 3 month limit on access to courses, and a 3-week limit on the individual 10-hour lessons.
You can also purchase an affordable 1-year membership to their library of digital content, which has thousands of books, audiobooks, databases, online dictionaries, and more for studying Spanish.
Although the user interface is not very modern, the Instituto Cervantes has some of the few online platforms that meticulously takes you through each of the CEFR levels with structured, high-quality, and interactive lessons. If you know you can motivate yourself to self-study and have some spare cash to invest in your learning, it will probably be time and money well spent. Unfortunately, each course must be purchased separately and they are quite expensive. You can take a look at the archived lessons here and decide if you want to purchase the full course to provide more structure.
Beginners may want to download the Readlang Chrome extension to help with translation, as most of the webpages are entirely in Spanish. Also, nothing beats learning through speaking the language, so check out italki, SpanishVIP, and Baselang for online Spanish tutors.