Message selection not working

I am unable to select multiple messages for deletion in the Messages app on the Mac mini (M1, 2020).

Is this a bug or am I doing something wrong? I have followed the procedures but selection does not work.

The Messages user guide states that to delete one or more messages we should be able to select one or more messages.

The modal window displays the following:

To select one or more items—such as contacts, emails, files, folders, or photos—do any of the following:

Select an item: Move the pointer over the item, then click it.

Select multiple items: Press and hold the Command key, then click the items.

Select multiple items that are next to each other: Click the first item you want to select, press and hold the Shift key, then click the last item.

You can also click near the first item, press and hold the mouse or trackpad, then drag over all of the items.

My device: Mac mini (M1, 2020)

OS: macOS Big Sur version 11.2.1 last checked 2/11/20@1145

Thanks for your help.