Version Used: commit 973b3aa
Steps to Reproduce:
Run the following code with net 6.0:
using System;
Console.WriteLine($"{{{12:X}}}");
See here
Expected Behavior:
It should print "{C}" like it did in net5.0
Actual Behavior:
It prints: "{X}}"
That there is parsing error is very good visible in Visual studios highlighting:

See csharplang discussion: here
Details
With net5.0 it was lowered to:
Console.WriteLine(string.Format("{{{0:X}}}", 12)); //prints "{C}"
but with net6.0 it is lowered to
DefaultInterpolatedStringHandler defaultInterpolatedStringHandler = new DefaultInterpolatedStringHandler(1, 1);
defaultInterpolatedStringHandler.AppendLiteral("{");
defaultInterpolatedStringHandler.AppendFormatted(12, "X}}");
Console.WriteLine(defaultInterpolatedStringHandler.ToStringAndClear()); //prints "{X}}"
instead of:
DefaultInterpolatedStringHandler defaultInterpolatedStringHandler = new DefaultInterpolatedStringHandler(2, 1);
defaultInterpolatedStringHandler.AppendLiteral("{");
defaultInterpolatedStringHandler.AppendFormatted(12, "X");
defaultInterpolatedStringHandler.AppendLiteral("}");
Console.WriteLine(defaultInterpolatedStringHandler.ToStringAndClear()); //prints "{C}"
Version Used: commit 973b3aa
Steps to Reproduce:
Run the following code with net 6.0:
See here
Expected Behavior:
It should print "{C}" like it did in net5.0
Actual Behavior:
It prints: "{X}}"
That there is parsing error is very good visible in Visual studios highlighting:

See csharplang discussion: here
Details
With net5.0 it was lowered to:
but with net6.0 it is lowered to
instead of: