Currently, due to database constraints, the limit for the URL field is 255 Characters. There is a public document JIRA throws an error when trying to insert an URL string longer than 255 characters in an URL Custom Field where the first workaround is to use a Text Field (multi-line) field type.
While testing this workaround, we noticed that the custom field of multiline text field type is not acting as a hyperlink. Whereas while using Description (a system multiline test field), if you input a string starting with 'http://' or 'https://', this field type will recognize as an URL and generate the hyperlink normally.
1. Tested with Description - a system field, - with description.png
2. Tested with "multiline custom text field type" - with custom field.png
The "multiline custom text field type" should recognize the input string as a URL if inputs with HTTP or HTTPS.
The "multiline custom text field type" recognizes the input string as a normal string even if inputs with HTTP or HTTPS.
By default the renderer of the multiline custom filed is "Default Text", please change the renderer to "Wiki type"