It doesn't matter what the file contains, as long as it exists. Any Dolphin build without its own portable.txt will store all its data in your Documents folder, so my recommendation would be to have your old build that you need to make specific games work portable and allow the latest access to the shared folder as the old build won't be changing, but whichever revision counts as 'latest; will change over time and you should ideally be using as new a revision as possible for everything.
Also, as for the original issue that's forcing you to use the old one for specific games, is it a known thing (e.g. posted on the wiki/the game's forum thread) if not, if it's not fixable in the latest dev, the developers will probably want a bug report so they know it's broken and can fix it.
Also, as for the original issue that's forcing you to use the old one for specific games, is it a known thing (e.g. posted on the wiki/the game's forum thread) if not, if it's not fixable in the latest dev, the developers will probably want a bug report so they know it's broken and can fix it.
OS: Windows 10 64 bit Professional
CPU: AMD Ryzen 5900X
RAM: 16GB
GPU: Radeon Vega 56
CPU: AMD Ryzen 5900X
RAM: 16GB
GPU: Radeon Vega 56