If / When you understand the different intents of the users that use different platforms you’ll be advertising to, it’s best to create different strategy plans for each target audience

If you’re selling a product/service continue to advertise to customers on Google Ads. When you have a sale and want to advertise awareness, use Facebook to expose it to as many interested parties as possible.

https://blog.brandrep.com/google-ads-vs-facebook-ads-which-should-you-use-for-your-business