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We have not. We moved to Defender on everything from W10 20H2 to S12 R2/S16 in our Citrix environment - infrastructure included - and it has been smooth. All exceptions from Citrix's guide are included.

good. Not sure by what this is caused right now, getting errors like "Microsoft Defender Antivirus Real-Time Protection feature has encountered an error and failed. - This may be due to low resource conditions". CPU is on 100% and msmpeng.exe using most of the resources. After a Defender Update CPU is not anymore on 100%, but some services are still crashing and brokeragent.exe fails.

Are you using FSL? We had servers going unresponsive fairly frequently and the latest FSL agent almost completely resolved it. We saw the same error messages that you are, but other services we're displaying the same resource utilization error.

Yes we are, version should be minimum 2201, not sure if the Hotfix has been applied. I'll let you know tomorrow.