In GA4, conversions are just events you decide are "key." The job is to ensure the right event exists and then mark it as a key event in GA4.
GA4 lets you create or modify events in the GA4 admin so you can turn something like a thank-you page view or a specific form-submit signal into an event, and then you flag that event as the one you care about for reporting and bidding.
For landing pages, the cleanest pattern is GA4 on the page, one event that represents a real completed lead (usually thank-you or confirmation), and that event marked as a key event. This avoids counting button clicks that never submit and gives you a stable metric you can later import into ad platforms if needed.
Install GA4, define the real completion event, and mark it as key. Do not mark clicks as conversions.