Hi again @Expiscornovus,
I have managed to create a flow (including all variables), but i'm struggling with json part from the post you mentioned.
I don't have a clue about json coding, but what i can read is that there is no reference to my File Viewer web part on the page. I see that by Use Case Title we can "navigate" to the page we want, but i don't get it how to point the code to specific File Viewer.
Additionally, i see the List is being used. But, i'm not sure how to change to to point to a Folder?
Also, i'm getting an error in the flow:
Correct to include a valid reference to 'Get_file_properties' for the input parameter(s) of action 'Send_an_HTTP_request_to_SharePoint
Current flow looks like this:

Step Send an HTTP request to SharePoint looks like this:

The code:
{"LayoutWebpartsContent":"[{\"id\":\"@{variables('PageTitleWebPartId')}\",\"instanceId\":\"@{variables('PageTitleWebPartId')}\",\"title\":\"\",\"description\":\"\",\"serverProcessedContent\":{\"htmlStrings\":{},\"searchablePlainTexts\":{},\"imageSources\":{},\"links\":{}},\"dataVersion\":\"1.4\",\"properties\":{\"title\":\"@{variables('Use Case Title')}\",\"imageSourceType\":4,\"layoutType\":\"FullWidthImage\",\"textAlignment\":\"Left\",\"showTopicHeader\":false,\"showPublishDate\":false,\"topicHeader\":\"\",\"authors\":[],\"authorByline\":[\"@{outputs('Get_file_properties')?['body/Author/Email']}\"]},\"reservedHeight\":228}]",
"CanvasContent1":"[{\"controlType\":3,\"id\":\"@{variables('CanvasContent1ControlId')}\",\"position\":{\"zoneIndex\":1,\"sectionIndex\":1,\"controlIndex\":1,\"layoutIndex\":1},\"webPartId\":\"@{variables('DocumentEmbedWebPartId')}\",\"webPartData\":{\"id\":\"@{variables('DocumentEmbedWebPartId')}\",\"instanceId\":\"@{variables('CanvasContent1ControlId')}\",\"title\":\"File viewer\",\"description\":\"\",\"serverProcessedContent\":{\"htmlStrings\":{},\"searchablePlainTexts\":{\"title\":\"@{outputs('Get_file_properties')?['body/{Name}']}\"},\"imageSources\":{},\"links\":{\"serverRelativeUrl\":\"@{replace(outputs('Get_file_properties')?['body/{Link}'], variables('RootUrl'), '')}\",\"wopiurl\":\"@{outputs('Get_file_properties')?['body/{Link}']}\"}},\"dataVersion\":\"1.4\",\"properties\":{\"annotation\":\"\",\"authorName\":\"@{outputs('Get_file_properties')?['body/Author/DisplayName']}\",\"chartitem\":\"\",\"endrange\":\"\",\"excelSettingsType\":\"\",\"file\":\"@{outputs('Get_file_properties')?['body/{Link}']}\",\"listId\":\"@{variables('FileViewerSourceListId')}\",\"modifiedAt\":\"@{utcNow()}\",\"photoUrl\":\"@{replace(outputs('Get_file_properties')?['body/Author/Picture'], concat(variables('SiteUrl'),'/_layouts/15/UserPhoto.aspx?Size=L'), '/_layouts/15/UserPhoto.aspx?Size=S')}\",\"rangeitem\":\"\",\"siteId\":\"@{variables('SiteId')}\",\"startPage\":1,\"startrange\":\"\",\"tableitem\":\"\",\"uniqueId\":\"@{replace(replace(split(outputs('Get_file_metadata')?['body/ETag'], ',')?[0], '"{', ''), '}', '')}\",\"wdallowinteractivity\":true,\"wdhidegridlines\":true,\"wdhideheaders\":true,\"webId\":\"@{variables('WebId')}\",\"webAbsoluteUrl\":\"@{variables('SiteUrl')}\"}},\"emphasis\":{},\"reservedHeight\":686,\"reservedWidth\":1180,\"addedFromPersistedData\":true},{\"controlType\":0,\"pageSettingsSlice\":{\"isDefaultDescription\":true,\"isDefaultThumbnail\":true}}]","AuthorByline":["@{outputs('Get_file_properties')?['body/Author/Email']}"],"TopicHeader":"","BannerImageUrl":"/_layouts/15/images/sitepagethumbnail.png","Title":"@{variables('Use Case Title')}"}