Why in Google Play 10.3.12 I have old layout? I have Google Play 10.3.12-all [0] [PR] 198814133 on Xiaomi Redmi Note 4 (with MIUI 9.5) and earlier I had the new layout of Store, but now I see that the old one came back.

Is this related to uncertified/rooted device?

I searched internet but I didn't find any answers.
Have you tried reinstalling Google play services?

https://www.google.dk/amp/s/www.androidpit.com/install-google-play-services-apk%3famp=true

Although I would like to point out that sometimes Google play store indeed does change some functions. Sometimes I see the downloads as text, sometimes I see it as an icon.