Hi and welcome @Mark_Evans!
This is absolutely possible. When you type in a cell of a linked field it searches the available records in the linked table. If it finds a matching record you can link it by clicking on it or use [Enter]. If the record doesn’t already exist you can manually click to add a new record or simply hit [Enter] to create a new record with the name you searhed for.
For you to simply be able to enter the URL and hit [Enter] or to search by URL you need to have the URL in the tables primary field (the first field from the left). If you use the primary field for anything else, you will first have to create a record and paste the URL into that new record. Both works well and is a matter of preference.