[ema]

Speaking is use it or lose it[1] but understanding stays. If you spend on average twenty minutes a day listening to content that is at a level where you understand most of it for twenty years at the end of it you will have no trouble understanding that language in most contexts. You can even have year long gaps as long as the average works out. Learning to understand a language isn't hard (if there's sufficient learner content) it just takes a lot of time. Of course if you have enough free time you can do 4 hours a day and get there in less than two years. Once you are at that level you are in an excellent position to learn to speak the language even if you have to repeat that part of the process if you leave long gaps.

If you want to give Spanish another go I can recommend dreamingspanish as they have just a ton of excellent learner content on various levels.

[1] to the point that I sometimes have trouble expressing certain concepts in my native German even though I live in Germany because so much of my life happens in other languages.