Execute an Identify Call in my Segment workspace from a Destination Function on the onPage event

This is very possible.

Here is a snippet from one of my destination functions that performs this action.

call.userId = user;
		call.anonymousId = anonymous;

		// Learn more at https://segment.com/docs/connections/spec/track/
		const endpoint = 'https://api.segment.io/v1/identify'; // replace with your endpoint
		let response;
		console.log(call);
		try {
			response = await fetch(endpoint, {
				method: 'POST',
				headers: {
					Authorization: `Basic ${btoa(settings.writeKey + ':')}`,
					'Content-Type': 'application/json'
				},
				body: JSON.stringify(call)
			});
		} catch (error) {
			// Retry on connection error
			throw new RetryError(error.message);
		}

		if (response.status >= 500 || response.status === 429) {
			// Retry on 5xx (server errors) and 429s (rate limits)
			throw new RetryError(`Failed with ${response.status}`);
		}