Yes. Lightroom-Classic can store up to five Custom Crop RATIOS.
When you [Enter Custom] you can state the ratio and it will store.
If you enter more that five custom ratios - the oldest is deleted. 'First in - First out'.

These are RATIOS only. To set the PIXEL dimensions you set the RESIZE options in the EXPORT dialog.
A RESIZE in the EXPORT dialog will FIT your image ( of any RATIO) into the PIXEL DIMENSIONS set.

Regards. My System: Windows-11, Lightroom-Classic 15.6, Photoshop 27.8, ACR 18.7, Lightroom 9.4, Lr-iOS 10.4.0, Bridge 16.0.3 .