You can't just rename the old .txt file. The format is completely different. For example:
{
"InstalledPluginNames": [
"Obsolete field, using only for compatibility"
],
"InstalledPlugins": [
{
"SystemName": "DiscountRequirement.MustBeAssignedToCustomerRole",
"Version": "1.34"
},
{
"SystemName": "CurrencyExchange.ECB",
"Version": "1.26"
},
{
"SystemName": "Misc.SendinBlue",
"Version": "3.26"
},
{
"SystemName": "Payments.CheckMoneyOrder",
"Version": "1.44"
},
{
"SystemName": "Payments.Manual",
"Version": "1.53"
},
{
"SystemName": "Payments.PayPalSmartPaymentButtons",
"Version": "1.13"
},
{
"SystemName": "Payments.PayPalStandard",
"Version": "1.60"
},
{
"SystemName": "Pickup.PickupInStore",
"Version": "1.34"
},
{
"SystemName": "Tax.Avalara",
"Version": "2.35"
},
{
"SystemName": "Tax.FixedOrByCountryStateZip",
"Version": "1.33"
},
{
"SystemName": "Widgets.FacebookPixel",
"Version": "1.02"
},
{
"SystemName": "Widgets.GoogleAnalytics",
"Version": "1.62"
},
{
"SystemName": "Widgets.NivoSlider",
"Version": "1.38"
},
{
"SystemName": "ExternalAuth.Facebook",
"Version": "1.63"
},
{
"SystemName": "Shipping.FedEx",
"Version": "1.36"
},
{
"SystemName": "Shipping.FixedByWeightByTotal",
"Version": "2.23"
},
{
"SystemName": "Shipping.USPS",
"Version": "1.47"
},
{
"SystemName": "Shipping.ShipStation",
"Version": "1.06"
}
],
"PluginNamesToUninstall": [],
"PluginNamesToDelete": [],
"PluginNamesToInstall": []
}