Cannot associate a "person" with an existing "user"

[ildar170975]

Checklist

• I have updated to the latest available Home Assistant version.
• I have cleared the cache of my browser.
• I have tried a different browser to see if it is related to my browser.
• I have tried reproducing the issue in safe mode to rule out problems with unsupported custom resources.

Describe the issue you are experiencing

A new HA setup (dev 2026.4).
While onboarding, a "user" was created:

Later a "person" was created (there were no "person" entities created automatically).
To associate the "person" with a "user", I toggled that switch:

And failed to proceed:

because on that step I was asked to create a NEW user instead of selecting an existing one.

In fact, this is an old issue, it was earlier reported (2021-2023) - #9811, #19127.
The only possible way to fix it - using yaml (posted here in the end of the post).
But due to a trend to move more things to UI (along with inability/laziness of some users to use yaml), perhaps we should consider the current mechanism as a serious "imperfection" - that is why the current issue was created.
P.S. Please, by chance, do not kill a currently available way to create persons via yaml, thank you.

Describe the behavior you expected

as above

Steps to reproduce the issue

as above

What version of Home Assistant Core has the issue?

2026.4 dev

What was the last working version of Home Assistant Core?

No response

In which browser are you experiencing the issue?

No response

Which operating system are you using to run this browser?

No response

State of relevant entities

Problem-relevant frontend configuration

JavaScript errors shown in your browser console/inspector

Additional information

No response