Hi TanyaSPG,
Thanks for sharing updates with us and I really appreciate your effort and your precious time doing those tests. First, please accept my apologize you meet such an issue and I understand it effort on your daily work.
We appreciate your understanding that sometimes the initial suggestions may not resolve the problem very soon. However, we can work together to narrow down and resolve the situation
Regarding to, "If I was to use solution 4, is it possible to also have the ability to 'edit' the document?" if you wish to use Solution 4, and also want user the ability to Edit document as well, the you may use below JSON code in update your column (File column).
{
"$schema": "https://developer.microsoft.com/json-schemas/sp/column-formatting.schema.json",
"elmType": "a",
"txtContent": "@currentField",
"attributes": {
"target": "_blank",
"href": "=if(indexOf([$ContentTypeId], '0x0120') >= 0, '?id=' + [$FileRef], @currentWeb + '/_layouts/15/Doc.aspx?sourcedoc='+ [$UniqueId] + '&action=View')"
}
}
Note: When user click on stored document in SharePoint online document library, it will open in View mode however in the top of document bar have "Edit button" click on it when users want to edit document.
I appreciate your understanding and stay safe!!
Best Regards
Waqas Muhammad