Most of it can be attributed to Modern Apps. Each Modern App also has a database sitting behind it, this will get recreated every time in non-persistent desktops.

The creation of the Start Tiles, which is also controlled by a database, further increases login time.

You might consider the following when using Windows 10 as a VDI OS, if you didn't done this already.

- Windows 10 LTSB (No new feature updates, only security, No Cortana, Store, Edge and Store Apps)

- When using UEM for profile management, use direct flex as much as possible to reduce logon times.

- Use VMware OS Optimization Tool like already mentioned in other replies. There is also a public template coming from LoginVSI with #VDILIKEAPRO https://labs.vmware.com/flings/vmware-os-optimization-tool

- Maybe you can try the Start Menu and Profile options listed here: https://4sysops.com/archives/improving-windows-10-logon-time/

- Remove OneDrive setup

The OneDrive setup executable is in the default user registry key, so this will always be automatically installed with each logon. (Thanks Microsoft)

This applies also for Windows 10 LTSB.

See: How to prevent OneDrive Setup prompt after first Log-In

- Check registry for RUN and Active Setup items

Good luck!