Really depends on each's usage.

My current Mi9T 64GB, with all photos ( i think 8 years total ) and some FLAC files, I still consistently have 15GB available.
I do have habit of clearing cache ( for some apps infamous of consuming storage, FB/IG/browser etc ) every 1-2 weeks 

If you are ex-Apple user, then you are going to need bigger storage as you kept restoring your phone. Personally I see my usage remained the same over the years. Hardly took any videos, just some pictures here and there. 64GB should be enough for most people provided they dont download GBs of games/movies.

it will show like this, see Post #728:

Maybe someone got the one with the cooler and cancelled his earlier order or something...

No... you bought the one without the cooler. Simple as that. There's no way to find it without the link.

The cooler is just a gimmick. The high price tag make you want to own it for free but in reality, it's just a peltier. What I can say is that you won't lose your sleep over it. Without physical touch between the internal heatsink and the peltier, it just basically cool the glass which gives you a fake temp reading. It's not the temp on the inside of the phone.

I bought this one, but it’s made of hard plastic and kinda sharp around the edges. Bit worried it might scratch the phone’s aluminium frame

Have you tried to exclude whatsapp from battery optimization and see if it happens again?
Sorry, another two things I forgot to mention,

1. You need to remember your password to unlock your lockscreen. Because at the start of TWRP custom recovery, you will be prompted to key in the same password to decrypt. Else flashing or wiping will fail.

2. By default, if I remember correctly, the provided twrp will be in Chinese language. It'd be no problem if you know to read Chinese language. Otherwise just google it to find the language changing guide for TWRP.

game mode ?
check whatsapp setting.
set auto start.
set allow wifi, 3/4g for sim 1 n 2.
Than miui AI will learn from it.
if u want hard way, lock the apps

go game configuration ....

I tried that still the same. Sometimes the wifi is not working properly. Not sure if its the phone settings because it doesnt happen to my other devices.

Have not tried playing other games but I have been playing this game called "Blade & Soul Revolution" specifically. After a while in the game I will get disconnected from Whatsapp but wechat is ok still connected.