This feature is build-in (prepared), but actually not enabled in the betas. - The final release version should offer and enable this interoperation feature then.
Some possibilities, today:
You can do some edits directly in Publisher, today. In the Layers panel you can select a layer, and then click the Adjustments icon at the bottom of the panel. Or the fx icon. Changes that you make will be done only in your Publisher document.
If what you want to do can't be handled by that, then you can use File > Edit in Photo and the document will close in Publisher and reopen in Affinity Photo positioned to that page. You can do your edit, use File > Save to save the file, and then manually reopen it in Publisher. Again, these changes are just in your Publisher document.
If you have a Linked image file (JPG, TIFF, PNG) in your Publisher document, and you select it with the Move Tool, there is an Edit Image button on the Context Toolbar. Clicking that will open just that image in a new tab in Publisher, where you can edit it using the tools available in Publisher. These changes will update the original linked document when you Save them.
In the future, as already mentioned, the Photo Persona will be available. Though we do not know for sure what it allows, I envision it as providing most of the functions of the Photo Persona in Affinity Photo.
There is also Typeface 2, which I have just discovered. It has some very nice ways to manage/create collections of fonts. And the added advantage, according to one reviewer on the Apple App Store of "Auto Activation in Affinity Apps (and others)." That was what sold me. It is half the price of RightFont as an added incentive.
