ive got my iphone 12 pro max, i feel like its draining battery faster and heating up so bad while use, while i used to have iphone 11 pro max , and wasnt like this, is there a problem in my new phone ?

iPhone 11 and later models, battery performance --> About the battery and performance of iPhone 11 and later

Try some of these options too.

1. Avoid Screen Mirroring
2. Put on Low Power Mode
3. Put Auto-Lock on (1 min):- with low power mode it will be 30 Sec
4. Put Auto Answer Off
5. Disable Push notifications for apps you do not use often
6. Keep your iPhone Facedown to prevent notifications to light up the screen
7. Enable Auto-Brightness:- Settings > General > Accessibility > Display Accommodations > Auto-Brightness [Enable]
8. Manually lower brightness from Control Center
9. If you Want to watch continuous Video. Stream it on TV or a Monitor
10. Don't force close apps; Apps which are not on frontend screen are paused by the system to save energy. Apps require more energy to re-launch. Apps which are open in the background use large memory is a myth and quitting them is counterproductive
11. Location services to be allowed only while using the app
12. Set your iPhone to fetch email and calendar data from internet less frequently
13. Turning off Background App Refresh 
14. Charge before it drops below 20-30%
15. Try connecting to trusted Wifi wherever available instead of Cellular
16. Enable Airplane mode in areas with bad cellular and wifi coverage. Your phone keeps trying for reconnection with the missing/weak network. This uses a lot of energy
17. Switch off Wifi & Bluetooth while in Roaming or Not in Range
18. Enable "Wifi Assist" : Settings > Cellular or Settings > Mobile Data > Wi-Fi Assist [Enable]
19. Periodically Check the Battery Health (Settings > Battery > Battery Health)

Surely the top of the range, massively expensive, brand new iphone shouldn’t need all these myriad changes just to work without overheating? One would have to question if it’s fit for purpose on this basis? I’m thinking of buying one and this is definitely putting me off.

So I see I’m not the only one having issues with the new iPhone 12 Pro Max. Battery draining in half a day. And back if phone gets really hot!! I went to apple store Baybrook mall and I was told to buy more GB for space. And is still the same.😡. Now I have to drive up there today again!! Like gas is so cheap!!!

I have the iPhone Promax 12 or vice-versa. I also have a new up to date I watch. My cell phone calls are coming through on the watch and not on the phone. I have a problem raising my arm, so I cannot answer the calls. This is cray-cray. Additionally, the watch needs to be charged twice daily. What's up? I've asked my techie sons and since they set up the watch--no reply there. Is it the watch face that I am using? Minnie Mouse? Just curious. I also hate the multiple steps to shut the phone off. it is difficult to do with the protective case. And, the T-Immobile store provided no tutoring on the phone. Disappointing.

I do have the same issue but I noticed it goes darker screen due to heat when it is on 5G and I am inside the house.

If one has to shut off as you suggested then why to but this Phone

My bff has the 12 and does not have the overheating issue that we are having. I am wondering if the issue is the charger?