All apps using significant energy on new machine, battery not charging (MBP 16", 2020)

The problem started with brand new machine MBP 16", 2020. Bought in late December 2019.

With full maximum specs at the time. 2,4 Ghz, 8-Core Intel Core i9, 64GB 2667 MHz DDR4, AMD Radeon Pro 5500M 4GB, 8TB SSD disc.

No matter which app I'm working on, the power drop-down tells me it is 'Using significant energy'. Usually there are multiple apps listed, and not just Chrome or energy-hungry apps, but also Mail, Word, Excel, Spotlight, Dropbox, Safari, etc even Display Brightness etc. Even if I have just one app open, it will always be flagged as using significant energy. This is the case whether the machine runs on battery or external power.

Also the vents are making a lot of noise very often and the mac is seemingly working on max power even if I don't do anything or do some little task.

I brought in the mac for service and even though they didn't found a hardware problem then they still changed the graphics card and logic board just in case. And installed the new Big Sur operating system.

Also overwrote the T1 chips firmware.

I also agreed not to transfer the soft from another mac but to install all the programs and accounts from scratch, so I could be sure there's no software issues.

But now when I started to set my mac app again – exactly the same problem occurred. So frustrating....

Also it often shows that the "BATTERY IS NOT CHARGING" and the power charge % is actually decreasing even though the power cord is attached. I tried with 4 different chargers. Or sometimes it shows that the charging takes 7 hours or something like that and the % is not moving but decreasing.

I understand that the battery might not charge at the time when mac is working with max CPU but my mac is almost always using max CPU even when it does some little task or almost nothing...

Has anyone had the same problem?

Can someone please help? :)

It's a very expensive machine, and not exactly what I had expected so far!