An option to prevent Google from combining data it collects on multiple services is to simply not sign into Google when using them. For example, if you're a Gmail user, you could log out of Gmail before using Google Search, Google Maps or YouTube.
Another, albeit tedious option, is to create separate Google accounts for each Google service that you use. For example, if you create a Google account only for Google searches, you could use that account when you'd prefer that Google not associate your searches with your primary Google account, such as your Gmail.
Google users who prefer not to receive personalized ads can opt out of ad personalization by visiting the Google Ads Preferences Manager. There, Google users will also be able to view (and change) the demographic information Google has gleaned from their search histories...