Is it possible to transform the **/*.tt file into a *.cs file. Using Azure Devops pipeline?
The answer is yes.
According to the state of the package T5.TextTransform.Tool:
T5 was a stopgap measure for a time when Mono.TextTemplating was not
available for .NET Core. Now that that is no longer the case, T5 is
not needed and no longer being maintained. Use Mono.TextTemplating's
dotnet-t4 instead.

So, we could use the Mono.TextTemplating instead of T5.TextTransform.Tool
.
Besides, there is also an implementation of the TextTransform.exe
command-line tool, we could use the command line to transform the .tt
file into .cs
file:
"%CommonProgramFiles%\Microsoft Shared\TextTemplating\1.2\texttransform.exe" -out %1.cs -P %2 -P "%ProgramFiles%\Reference Assemblies\Microsoft\Framework\v3.5" %1.tt
Check this thread for some more details.
Hope this helps.