Set the precision to be maximum of 28 (Jet limit).

When using property.HasConversion<decimal>() the default for EF Core is with precision 38 and scale 17 which is passed Jet's limit

src/EFCore.Jet/Storage/Internal/JetDecimalTypeMapping.cs

@@ -53,7 +53,20 @@ namespace EntityFrameworkCore.Jet.Storage.Internal
         ///     doing so can result in application failures when updating to a new Entity Framework Core release.
         /// </summary>
         protected override RelationalTypeMapping Clone(RelationalTypeMappingParameters parameters)
-            => new JetDecimalTypeMapping(parameters);
+        {
+            var precision = parameters.Precision;
+            var scale = parameters.Scale;
+            if (parameters.Precision is > 28)
+            {
+                int prec_diff = parameters.Precision.Value - 28;
+                precision = 28;
+                if (parameters.Scale is > 28)
+                {
+                    scale = parameters.Scale.Value - prec_diff;
+                }
+            }
+            return new JetDecimalTypeMapping(parameters.WithPrecisionAndScale(precision, scale));
+        }
 
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to

test/EFCore.Jet.FunctionalTests/config.json

@@ -1,7 +1,7 @@
 {
-    "Test": {
+  "Test": {
-      "Jet": {
+    "Jet": {
-        "DefaultConnection": "DBQ=Jet.accdb"
+      "DefaultConnection": "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=Jet.accdb;Persist Security Info=False;"
-      }
     }
+  }
 }