These answers are all a bit overly complicated.
<observer name="switch_currency_gbp" instance="Vendor\Module\Observer\CurrencyCheck" />
class CurrencyCheck ...
I was having the same issue in magento 2.3.7-p1. In logs, it was showing this error:
main.WARNING: Session size of 370635 exceeded allowed session max size of 256000.  
To fix this, run below command:
php bin/magento config:set system/security/max_session_size_admin 0
After cache flush, I was able to add products to shopping cart from admin order ...
You should be able to get the data you want by using the collection:
Magento is implementing the grid in your screenshot in this file:
where you should be able to get examples on how to implement it (with filters).
Create Indices for all custom columns which are used in grid/filter rendering.
To Create Indices in SQL table example.
CREATE INDEX SALES_ORDER_GRID_DEVICE_USED ON sales_order_grid (device_used)
After Creating all Indices run full re-indexing and cache clean commands.
php bin/magento indexer:reindex
php bin/magento cache:clean
Compare the results with old ...