tl;dr (quoted from the email, full below):

* If you are an individual developer declared as a trader, provide and verify a public phone number. Please be aware that your phone number and address will be displayed publicly on Google Play.

* You’re typically considered a trader under European Economic Area (EEA) and United Kingdom (UK) laws if you engage in commercial activities, including when you earn revenue from your apps (such as paid downloads, in-app products, subscriptions, or ads).

* If you don't complete your trader status declaration by the deadline, you won't be able to submit app updates, and your developer profile and all apps will be removed from Google Play globally.

* You must declare your trader status in Play Console, regardless of where you’re located.

Email from Google Play received 7 hours ago:

Hi <developer>,

Updated Google Play policies now require you to declare whether you’re a trader or non-trader in Play Console.

What you need to know

You must declare your trader status in Play Console, regardless of where you’re located.

You’re typically considered a trader under European Economic Area (EEA) and United Kingdom (UK) laws if you engage in commercial activities, including when you earn revenue from your apps (such as paid downloads, in-app products, subscriptions, or ads). If you operate purely as a hobbyist or in a non-commercial capacity, you can declare as a non-trader.

If you don’t distribute apps in the EEA or UK, you can declare as a non-trader.

What this means for you

You must complete your trader status declaration in Google Play Console by February 1, 2027:

Declare your trader status

1. Sign in to Google Play Console.

2. Go to Manage account > Account details > About you.

3. Under Trader status, select Declare your trader status and choose whether you are a trader or non-trader.

4. If you are an individual developer declared as a trader, provide and verify a public phone number. Please be aware that your phone number and address will be displayed publicly on Google Play.

5. If you declare as a trader, certify commitment to compliance with local laws.

6. Review your profile details and click Save.

If you don't complete your trader status declaration by the deadline, you won't be able to submit app updates, and your developer profile and all apps will be removed from Google Play globally.

Also documented here: https://support.google.com/googleplay/android-developer/answer/17594752