I have mentioned this previously...

We have received sporadic reports of this problem over several years. We have yet to have found the source of the issue. The image sequence codec is based off of a Windows component, so we suspect it is due to an issue with how VEGAS tries to access this component, however we have not been able to reproduce the problem locally. Contacting support is exactly what we would suggest so we can grab as much data as possible to help us finally diagnose the problem.

I contacted support offering to give my logs and they just told me roll back to Windows 10 like that's even a possibility. Wow looks like they're really looking for a fix.

Under Win 10 the option is selectable for me.

While the issue is fixed you can use the old Image Sequence script. I am attaching it in case it helps.

https://drive.google.com/file/d/1GuPeF17b28VYEEVI8yoOHBt7jnjedll4/view?usp=share_link

@juan_rios the same script that was discussed in this thread?

After working with the tech folks for Vegas, my issue was fixed and should have been provided in a Vegas 19 update. I remember seeing it in what was corrected in an update.

So my issue is resolved.

@juan_rios the same script that was discussed in this thread?

Yes; for another reason.

Installing `HEIF Image Extensions` also solves this problem.

I had the same problem, I solved it like this - Installing a sequence in Vegas 19
Enable DEVELOPER MODE before installation:

Parameters
Update and Security
For developers
Developer Mode - Install applications from any source,,,

enter the add-appxpackage command on behalf of the administrator (file name path command)
example:
in Windows PowerShell
 add-appxpackage C:\Users\User\Downloads\heif-image-extensions-1-0-60431-0.appxbundle

Really frustrating, I am one of those that makes constant use of it.

This seems like a Windows 11 exclusive problem on my end, no issues with Windows 10. I have two Windows 11 devices, one is a custom skylake desktop with Windows 11 insider and the other that is a laptop that has Windows 11. Vegas 18 on both of those machines, I have Vegas 13 as well and even that is missing the option.

Most solutions online call for installing HEIF image extensions. Uninstalling through powershell and reinstalling didn't help, the same with reinstalling HEVC.

The script juan_rios shared definitely does work but its too slow for me, I ended up rendering as a .mov file and converting it to a png sequence:

1. Once you finish your composition, go to File --> Render As
2. Select Apple ProRes and edit/Customize any one of the Templates
3. In the Video tab, change the "Frame size" and "Frame Rate" to your project's, strip away any audio from the Audio tab as well.
4. Back in the Video tab, the Profile will need to be "ProRes 444" if you are exporting to a transparent format, when selected, the "Include alpha" will be selectable, make sure that is checked since that is the trasparency.
5. Press ok and save the mov file
6. For this, you will need FFMPEG, assuming you named your file "filename.mov" run the command:
   ffmpeg -i filename.mov -q:v 0 output_%04d.png
7. Running the command above will generate a png sequence with the file names: "output_0001.png", "output_0002.png" and so on.

Its important to note that mov is not a lossless file format but there isn't much artifacting that I notice with the quality being on par with the preview exports. A faster workaround but its storage hungry.