A “no decision” means that the private revelation is not approved and it is not disapproved. Since it is not disapproved, you can believe in it if you want, but the Church is not going to promote or endorse it in any way. And there is a chance it may be disapproved in the future.
Some “no decision” private revelations get approved much later. For example, I’m aware of some cases of “no decision” private revelations where the person who received the private revelation has an open sainthood cause. If the person is ever beatified, then the private revelation would be considered approved. I’m also aware of another case where it took over 100 years for a bishop to approve the revelation but he finally did, and it is approved as of today. And a third case where the archbishop at the time had approved the revelations for faith expression and might well have approved the revelation entirely, but he died too soon before he had a chance, and the archbishops who came in after him haven’t been interested.
Those of us who are interested in private revelations will usually read up on the history of them and see what the revelation is alleged to have said, and make our own decisions about whether this is something we think is good and healthy for a Catholic to ponder about and maybe practice related devotions. If the revelation has been “approved for faith expression”, that means we’re allowed to say prayers and do devotions associated with it, even if the revelation itself is a “no decision”. There are a lot of private revelations in the “approved for faith expression” category and some of them have very active prayer groups devoted to them, with diocesan approval.
But obviously all this is the sort of thing that takes some careful research and study and is not just a matter of seeing some video on Youtube and jumping to a conclusion about it.