I agree - on my Mi 9T pro "raphael" I also have a really bad battery life. It may be Android 10, it may be MIUI 11, I don't know, but the fact is, I never (even without using the phone at all) achieve less than 3% battery use per hour. All settings (e.g. autostart, AOD, battery optimization etc) have been checked and adjusted to reduce the battery use as much as possible, and it did help: from >5% per hour, to 3.x% per hour. So, some improvement, but WAY to little.
I have also installed Greenify and Naptime to see whether they can help, but they don't do a lot on my device. For comparison, I have a Blackview BV9600, and with the same optimizations it has around 0.2% battery use per hour, and even with quite some use I get almost 3 days out of the battery (standby without use is 10 days or slightly more, reminding me of the Nokia days back in the early 2000s).
So, what's the problem? I have a few observations, which may explain it in parts, but there is - unfortunately - nothing we can do as users (even root users):
1. MIUI does not care about "start in the background" permission. You can revoke the permission for apps, but they do start in the background anyway. It works for many apps, but not for all, totally inconsistently. One app where it just doesn't work at all is Tripadvisor, just to give one example. It has always been like this, as long as I can remember MIUI. Well, at least consequently, this setting is not even present anymore in MIUI11 on Android 10...
2. In MIUI, doze does not work properly. Even when the device is in deep doze, it is active in the background a lot. As per Google design, the device should briefly wake up for maintenance intervals, but MIUI devices are much more active than they should (compared to other brand devices such as the BV9600 mentioned above).
3. I have used BetterBatteryStats to identify apps that cause excessive wakelocks, and disabled or uninstalled apps that I don't really need, but this still doesn't give a strong boost to battery life.
4. The only (but very efficient!) way to reduce the massive battery use is a "night mode" that I made myself as an automated task (GPS, WLAN, Bluetooth, Sync: off, Airplane mode: on). With these settings, energy consumption goes down to 0.3% per hour or so, thus saving 90% of battery! I have tried to find out which of my settings cause these massive battery saving I am observing, but haven't yet found out what it is. I keep investigating, but it takes quite a while to see the potential effect, and during the day I cannot switch off these things just for trying out things... If others here can add own experiences, we'd find out more quickly.