N/A

On pro plan you pay 20 dollar per person in your team, 1 Member Seats means your team only has one member and therefor you only pay 20 dollars

I guess that's recent cause I haven't changed anything on my end

that is bizarre

are you on pro plan?

yea

but anyway doesnt matter

The 20 dollar charge has always been a thing, that's not recent; it's very strange that you've only been charged 20 dollars extra recently

just wanted to figure out, so the base pay is 20$ and the usage is additional cost, correct?

yes that is correct

ok

maybe Im doing a thread hijacking now, but is it possible to downgrade from pro to hobby?

of course, you'd want to get a hobby plan from
once you've gotten a hobby plan you can migrate your pro plan projects over to your hobby account
Once everything is transfered you can cancel your pro plan

you can transfer projects between accounts by going to your project's general settings, there'll be an option to transfer at the bottom