Error when installing Lubuntu

I got Error when installing Lubuntu error is :

The installer failed to create partition on disk 'TOSHIBA MQ01ABD050'.

=... Create a new partition (109.99 GiB, ext4) on ‘/dev/sda’ 
=... Job: Create new partition on device ‘/dev/sda’ 
=... Command: sfdisk --force --append /dev/sda 
=... Failed to add partition ‘New Partition’ to device ‘/dev/sda’. 
=... Failed to add partition ‘New Partition’ to device ‘/dev/sda’. 

You haven't said which release you're trying to install, but if you check release notes (eg. Lubuntu 20.04.3) you'll find a Known Issues section

Replace Partition on Certain Partition Schemes With Calamares Fails

Installs replacing a partition may fail with this bug. As a workaround; reboot, use KDE Partition Manager to delete the ‘unknown’ partition that exists, create the partition using the format you want (ext4, btrfs & xfs were tested & worked), deactivate swap partitions & exit KDE Partition Manager. Calamares can then use the prepared partition.

You'll note that bug applies to "sfdisk --force --append /dev/sda" which is the message you've posted.

In discussion of the impish release notes this issue came up, and I've written the following which maybe helpful - https://discourse.lubuntu.me/t/calamares-rare-failure-to-create-partition-mkfs-errors/2774 . Summary steps are :-

  1. Reboot your live session.
  2. Delete & Re-create your system partition (using KDE Partition Manager)
  3. Repeat the install but keep your / partition (prepared in step 2)