Google Ads bids best when it knows which clicks turned into revenue. Tag-based conversion tracking only sees what happens in the browser, so phone deals, CRM sales and refunds are invisible to it.
Start with an account-level final URL suffix that adds campaign, ad group and ad ids to every click, including Performance Max and YouTube. Capture gclid, gbraid and wbraid on landing and keep them with the person's journey. Then upload purchases and leads as offline conversions with the click id and value, and add hashed email and phone as enhanced conversions so Google can match conversions even without a click id.