display does not go into sleep mode after OS upgrade big sur

Test to see if the problem is also present: a) in Safe Mode, and b) when logged in to a new user account

Please run Etrecheck and post its full report here. Use the "additional text" button and paste the report into the text box.

It may be a one-off incident, but you do have a lot of old stuff that may cause issues with the more recent OS.

[Not Loaded] LaCieScsiType00.kext - com.LaCie.ScsiType00 (1.9.1 - SDK 10.5)

[Not Loaded] hp_io_printerclassdriver_enabler.kext - com.hp.hpio.hp-io-printerclassdriver-enabler (19.16.0 - SDK 10.10)

[Not Loaded] hp_fax_io.kext - com.hp.kext.hp-fax-io (5.22.0 - SDK 10.9)

[Loaded] ufsd_NTFS.kext - com.paragon-software.filesystems.ntfs (15.5.90 - SDK 10.10)

[Not Loaded] Seagate Storage Driver.kext - com.seagate.driver.PowSecDriverCore (5.2.7 (26995) - SDK 10.4)

[Not Loaded] BJUSBLoad.kext - jp.co.canon.bj.print.BJUSBLoad (10.75.21 - SDK 10.8)

[Not Loaded] CIJUSBLoad.kext - jp.co.canon.ij.print.CIJUSBLoad (16.0.10 - SDK 10.9)

The Lacie and Seagate stuff is very old, and not needed. Your mac does not need third party drive vendor software.

The Paragon software is needed if you want to read and write to NTFS formatted drives, but if you use make sure it is fully up to date.

[Edit: it seems to be]