Google Ads is expanding Lookalike segments to Video campaigns, giving advertisers another campaign type where they can reach new users who share characteristics with existing audiences.
Previously, Lookalike segments were available only for Demand Gen campaigns. The expansion means advertisers running Video campaigns can now use their existing audience data to find and reach similar potential customers.

Google recommends using at least 1,000 active users in the seed list for better audience quality and recommends using value based data when available.
Read the official help page spotted by Hana Kobzová here: Use Lookalike segments in Video campaigns.