Currently, the custom field checkbox or the Drop down list in team managed projects is only limited to 55 options. 

A suggestion would be to increase it to allow users to have more options to be selected

Workaround

Since early 2023, global or Company-managed custom fields can be used in Team-managed projects (see the announcement here). The global custom field does not have the 55 options limit. The procedure would be:

1.  Create a new global custom field
2. Search and add the new custom field to the Team-managed project issue type