My brand new macbook air 2020 not charging and facing lags and bugs

Batteries are considered Consumable Products. Over time it will degrade to a point where it needs to be replaced. The usage is normal as the capacity will go up and down all the time and never stay always at 100%. Apple Batteries are rated for 1000 Full Battery Cycles and / or 80% Capacity before needing Evaluation or replacement.

For additional reading on Battery and Apple Computers this link may help. About battery health management in Mac notebooks and especially for the M1 and Big Sur  & Monterey If battery charging is paused or on hold on your Mac

Depending on the Age of the computer, some aspects from the above links, may or may not apply to your computer.

A feature introduced into Big Sur & Monterey was to preserve the number of Full Battery Cycles - there was an Algorithm coded into the macOS. It is perfectly Normal for Big Sur , Monterey to Pause / Suspend charging the battery beyond 80% and hold it at that level. One can nudge / over-ride this by clicking the Battery Icon on Desktop Top Bar and allow charging beyond 80%. From observations, it will Pause / Suspend again once reading 90%. Same procedure to over-ride and will charge to 100%

I think it's a problem with the hardware, but maybe I'm wrong. I suggest you do the Apple Diagnostics to see if it finds a problem with the hardware. Click the link inside the link about the reference codes. They say what the reference code you get means. I hope it doesn't take like 20 mins to go to apple diagnostics though. I think you should contact apple support too.

So just be absolutely clear - you just got is recently as Brand New or Refurbished or Second Hand.

From whom?

Catalina was released October 7, 2019 that is 2 1/2 years ago.

If I were you, I would return it to the Store or person from whom it was purchased and request a FULL REFUND

Apple does not offer a MBA 2020 with Catalina still installed if purchased in 2022 not even a Refurbished Directly from Apple would have Catalina

It must be an old/Second hand MacBook, and not new. Whoever you got it from, must have put this on sale because of it's problem. I don't know if they mentioned if the MacBook had problems, but if they said that it was new...they must be lying big time. I agree with P. Philips here about the refund part. This is not right.

Brand new from Apple ? The it would be running Big Sur macOS 11 or Monterey macOS 12 and not Catalina where is question is placed

Explain what version is installed please