Apparently, Google is ramping up the SERP page and testing for the dark mode of Google Search, before releasing a larger feature rollout. One of the favourite new additions of late 2019 and early 2020 was the dark mode, with the dark theme coming from the previous year of the most popular applications and services.
The dark mode of Google Search for desktop computers was first established in alpha and beta testing rounds.
According to the reports, for Google Search Dark Mode, Google could be widening its trial circle to more users, and the same now appears across a broader range of users.
Nonetheless, it remains uncertain, however, how common the dark mode experiments of Google Search are being carried out.
Reports have that the selection remains entirely random as of now, which seems to hold true for Indian users as well.
Right now, there does not appear to be an option to activate the dark theme while those [having the dark mode option available] can retain the dark theme preference.