I can't turn on memory integrity in Windows 11 even though no incompatible drivers are listed.

I should have added I moved my system image from a dying Dell to another brand laptop and had already deleted all the Dell apps, so didn't have that concern.

You might consider creating a system image (Control Panel -> File History -> System Image Backup -> Create a system image) before deleting any of them, and perhaps take a guess at which ones you could delete without impacting hardware and trying to enable Core Isolation after each deletion. Here are the five enumerated drivers from Dell that were on my system (Windows 7 -> Windows 10 -> Windows 11 following migration to new hardware):

Published Name: oem95.inf

Original Name: dddriver64dcsa.inf

Provider Name: Dell Technologies

Class Name: System

Class GUID: {4d36e97d-e325-11ce-bfc1-08002be10318}

Driver Version: 07/26/2021 2.0.6.0

Signer Name: Microsoft Windows Hardware Compatibility Publisher

Published Name: oem22.inf

Original Name: firmware.inf

Provider Name: Dell, Inc.

Class Name: Firmware

Class GUID: {f2e7dd72-6468-4e36-b6f1-6488f42c1b52}

Driver Version: 01/18/2019 1.27.0.0

Signer Name: Microsoft Windows Hardware Compatibility Publisher

Published Name: oem98.inf

Original Name: dellinstrumentation.inf

Provider Name: Dell Technologies

Class Name: DellInstrumentation

Class GUID: {e1c7dabe-63de-4630-a4de-a4adc0503be3}

Driver Version: 08/25/2023 2.8.9.4

Signer Name: Microsoft Windows Hardware Compatibility Publisher

Published Name: oem168.inf

Original Name: dellinstrumentation.inf

Provider Name: Dell Technologies

Class Name: DellInstrumentation

Class GUID: {e1c7dabe-63de-4630-a4de-a4adc0503be3}

Driver Version: 04/14/2022 2.8.5.0

Signer Name: Microsoft Windows Hardware Compatibility Publisher

Published Name: oem163.inf

Original Name: dellinstrumentation.inf

Provider Name: Dell Technologies

Class Name: DellInstrumentation

Class GUID: {e1c7dabe-63de-4630-a4de-a4adc0503be3}

Driver Version: 03/01/2023 2.8.9.3

Signer Name: Microsoft Windows Hardware Compatibility Publisher

P.S. don't ask why I didn't just start with a fresh OS install, but probably anyone reading this is in a similar boat ;-).

Just to say I tried a fresh OS install and it still didn't help although now at least MSE virus protection doesn't see the memory integrity being off as a problem. Before it came up orange and told me I wasn't protected.

Having spoken to other professionals on this I think it really doesn't matter if memory integrity is off. Its probably another thing that MS thought to be a good idea but didn't give the developers enough time to finish testing before release. It would be nice if they would just say this. There you go Mr Microsoft - I'll do your job for you !!