vivoactive 4 (all versions) SW 5.10

So you can't use a different watch face with 5.10 without the battery drain?

I can't.
I tried using 3 different IQ watch faces and they all drain the battery higher than the stock one, which wasn't the case prior to the update.

After few days running on 5.0, and several sync with the phone, yesterday the watch asked to upgrade to 5.1. I pressed "cancel" and the watch showed that the upgrade would be done overnight. 

As said by @Martin , I connected the phone to the computer,  edited the .GDC file with text editor,  deleting all the content inside and saved it back to the same location. 

No upgrade overnight. I'm still in 5.0

It's kind of interesting why the update seems to be stalled at 20%. Or maybe Garmin just forgot to upgrade this thread. Otherwise, this could indicate that the update maybe has stopped due to issues/problems.

I think it's just Garmin being under staffed to do an adequate job editing on the forums.

The Venu forum has this same update that wasn't even updated to read Venu... it still reads Vivoactive 4 to this day.

If you check multiple forums, the update roll out process often doesn't get fully updated, or better said, since lockdown it's not been updated past the initial post of 20% roll-out

To answer an above comment on contacting support and whether they will admit to issues. Garmin, much like any companies, are probably very careful to admit to issues even if they know there are. It's probably a liability thing. Secondly, Garmin support gives canned answers like, "we have not seen any issues based on our internal testing" 
A recent example written to me via email from the beta team reads, "We haven't seen any excessive battery drain in our testing, additionally this is a very complicated issue..." 

Their tester user base is probably tiny. The consumer base is huge, and the consumers that end up having an issue and posting here is also not going to be huge. But there is an obvious trend with Garmin and software reliability. Its obvious across all Garmin products in my household, and those of friends and family. Definitely a problem, and it usually takes more than a year for a device to have relatively OK software, and that is isn't always the case. 

So, like many companies, their customer support leaves little to be desired when it comes to honesty. The way the PR team handled communication with customers regarding the recent hack should paint the picture. 

All I can say is that this 5.1 update does have issues with various IQ apps, widgets and clock faces... My device is set up close to stock, with only two IQ watch faces that are actively updated by the developers. My battery consumption is not out fo the ordinary.

One thing I have noticed with the 5.1 update is a lot more disconnect/connect notifications from the watch. More specifically, these connections with the app and not the phone. I've now disabled phone connection, and last night my battery drain was 2% for a 8hour sleep apposed to the normal 5-6%.

Bluetooth connection to the phone is often another big battery culprit...

The updates for VA4 have been as follows according to gpsinformation.net

You can find a rough pattern here with regard to update intervals.

Ver. 5.10 - 09/09/2020

Ver. 5.00 - 08/19/2020

Ver. 4.90 - 07/14/2020

Ver. 4.60 - 05/14/2020

Ver. 4.50 - 03/11/2020

Ver. 4.40 - 03/11/2020

Ver. 4.00 - 01/20/2020

Ver. 3.80 - 12/17/2019

Ver. 3.60 - 11/13/2019

I chatted with "Kevin" via support chat who told me

Kevin:Ok it appears we will need to replace your watch at this time. I am going to create the order and it will be sent to your email so that you can complete and send back to our warehouse. We have two options in regards to the exchange so please let me know which one you prefer.

This was after I explained that this issue started with the latest firmware and I also gave him a link to this thread and told him multiple people are having the issue.

I declined to exchange.

That seems to be their response for a lot of things, I contacted them about GPS accuracy issues and they sent me a new watch (no difference). In fairness they are very good at exchanging/replacing, pity their forum engagement isn't as good!

Today in the morning (started with 62%) I did a factory reset, and installed 5.10 again. I didn't changed the watchface and 12 hours later I just lost 10%. So it's pretty much a normal battery consumption. I'll change the watchface tomorrow morning and will check the battery again.