About current vs last for some panels

I was running grafana 7.3.6 and recently upgraded to 9.0.5; The datasource of my grafana is prometheus

well, the settings of alerts changed completely, I am still trying to figure out the changes that I need to make to my alerts becase I am getting a ton of useless info in my alerts (email and telegram) and I am finding this not very intuitive. before you could define a threshold and you would see the red line with the little heart, … and this idea changed completely. if anyone can provide a guide on how to understand the new alerts and maybe migrate, I would appreciate

my main point for this thread:
In legend, I used to see the current value, so if I was getting nothing I would customize it to character -

In this version, I dont see current anymore, Now we have last and last*; so if I use either of them, I would get the last value but the problem is that last does not show - for no value, so it would show the last non-null value, basically the same as for last*,

in other words, no matter if I use last or last*, even when there is no value, it would still show the last value

can anyone explain whats going on?

ps: if I change in the query from range to instant, it would show the current value, but the graph would disappear. I admit that I am very confused with most of these changes