I don't recommend making a massive 90 item dropdown. The UI isn't really designed for such a scenario. There's 4 inputs per item in the UI so that's 360 inputs. It's possible you'll hit PHP input limits are the processing behavior could go bonkers having to loop through all of it. When you've a dropdown that large it's best to consider an external storage like a custom database table the building the dropdown using CB Query Field and its Query Select fieldtype.

I also don't recommend such a large list as it's typically bad UX. They're very hard for users to navigate and are near impossible on mobile. You may want to reconsider the field entirely to see if there's a simpler way to do what you're wanting. For example one great solution is Autocomplete. You can use a Text field with CB Query Field and its Query Autocomplete to query a custom database of values. When the user starts typing it can suggest a value to autocomplete the field.

At any rate have added a bug ticket to see if there's something we can do about large lists like that.

forge.joomlapolis.com/issues/7921

A custom database combined with CB Query Field and its Query Select would be the best option then. So for example you could have the below database table.

id | label | value | group

You could then build a select from those stored values. I have added a bug ticket to see if we can further improve how field values are created and stored, but it's not really designed for such a large amount of options.