Slow when using brush in mask

Hi. Recently LRC has been quite slow working on my imac. But it gets a lot worse as soon as I try using a brush in a mask. After a few brush strokes it start stalling, the image becomes pixelated and it is almost impossible to continue working. If I delete that mask it is better again. I watch my activity monitor while this happens and it the CPU is on overload running at some insane 500%. I saw some threads on similar subject but not with mac.

Any idea how to fix that would be great. Thanks

My system :

Processor: 3.1 GHz 6-Core Intel Core i5

Graphics: Radeon Pro 575X 4 GB

Memory: 64 GB 2667 MHz DDR4

And all the performance info:

Lightroom Classic version: 13.0.1 [ 202310121438-d2af310c ]

License: Creative Cloud

Language setting: en

Operating system: Mac OS 13

Version: 13.6.1 [22G313]

Application architecture: x64

Logical processor count: 6

Processor speed: 3.1GHz

SqLite Version: 3.36.0

Built-in memory: 65,536.0 MB

Real memory available to Lightroom: 65,536.0 MB

Real memory used by Lightroom: 15,837.4 MB (24.1%)

Virtual memory used by Lightroom: 84,461.1 MB

Memory cache size: 1,100.5MB

Internal Camera Raw version: 16.0 [ 1677 ]

Maximum thread count used by Camera Raw: 4

Camera Raw SIMD optimization: SSE2,AVX,AVX2

Camera Raw virtual memory: 2235MB / 32767MB (6%)

Camera Raw real memory: 2353MB / 65536MB (3%)

Standard Preview Size: 4096 pixels

Displays: 1) 4096x2304

Graphics Processor Info: 

Metal: AMD Radeon Pro 575X

Init State: GPU for Image Processing supported by default

User Preference: GPU for Export enabled

Application folder: /Applications/Adobe Lightroom Classic

Library Path: /Volumes/Extreme SSD/Lightroom/LR catalogue/Lightroom/Lightroom Catalog-v13.lrcat

Settings Folder: /Users/Florence/Library/Application Support/Adobe/Lightroom

Installed Plugins: 

1) AdobeStock

2) Aperture/iPhoto Importer Plug-in

3) Flickr

4) Nikon Tether Plugin

Config.lua flags: None