SolarWinds License

Hello! I am new to SolarWinds products. Thanks to your help, I came to know that, there are two type of licensing; perpetual based and subscription based. Then my question is, what is licensing tier for? Like for example what I have seen is, SolarWinds Observability has 6 type of products. like log observability per GB per month. Does this means it is subscription based? And on the other hand, hybrid cloud observability has essentials and advanced and there is license tires. I am in confusion.