In my own extension I have extended fe_user table to add some relations for users to sysfolders (pages with doktype 254). I did it with common TCA override and adding the group type. In general that works for normal amount of records (like several tens or so) but in some cases some users can have chosen up to 3000+ relations.

Unfortunately, in such case TYPO3 BE doesn't render these relations in form properly (it's empty, although database contains a list of 3000 comma-separated UIDs and FE plugins displays these relations properly).

Of course in such case after saving the form in BE causes that the DB column is cleared.

As you can see, I tried to increase the maxitems without result. Is there some other config option that I missed, or for such huge amount I should use another type of form field? Any advice will be highly appreciated.

File typo3conf/ext/myext/Configuration/TCA/Overrides/fe_users.php

'tx_myext_points' => [
    'exclude' => 0,
    'label'   => 'Sale points for user',
    'config'  => [
        'type' => 'group',
        'internal_type' => 'db',
        'allowed' => 'pages',
        'maxitems' => 999999,
        'suggestOptions' => [
            'default' => [
                'searchWholePhrase' => 1
            ],
            'pages' => [
                'searchCondition' => 'doktype = 254'
            ]
        ]
    ]
],