What happens if one didn't finish their missed prayers before current prayer?

I was searching about how to make missed prayers and learnt that If missed prayers are less than 6 prayers it should be prayed before the current prayer.

I knew that before too but i hadn't thought if i didn't pray missed prayers beforehand my current prayer will be invalid. I'm not sure about this information but if that's the case do i have to pray those "current prayers" i mentioned as a missed prayers. I don't remember which one was which but i am so anxious 😭

And where did that 6 prayers rule come from. Wherever I searched they always say that without any resources like Hadith or surah.

edit:OK GUYS IT WAS A MISINFORMATION! This "less than 6 prayers" rule is for someone who has been praying since puberty with 5 missed prayers. That person is named "sahibi tertip" in my language but i don't know its name in english. For example if you have 20 missed prayers and you prayed those until it's 5 missed prayers you still don't have to pray that until the next prayer. There are more opinions regarding that but these are the things I understood.