I too have the same problem while searching for hundreds of products in inventory, I have found an addon in the app store that is working well, try it.

Multi Search | Odoo Apps Store

I'm also looking for an answer for this. I want to do an AND not an OR search without having to click and do a Custom filter.  This should be an easy thing... The OR search is just type something, hit enter, then type the next thing and hit enter.
I haven't figured out a AND search yet. It's obviously possible to do AND searches because you can do it from the Add Custom Filter. This is a slow process and something I do multiple times per day.

(Currently running Odoo 16.4 SAAS)

Also I have same problem. You are right I can hit enter and then write other product name. So what if I have a hundred of product names. How can I search all product at once? For example in SAP there is a button for multiple searcing. You can click the button and then add product name on a table, and also you can import from an excel table. How can I do this in Odoo?

Do you mean A OR B?

Enter the first search term, hit ENTER.

Enter the second search term, hit ENTER.

Try with advanced search, select the field and value, then add condition with same field and the other value, then it makes "OR" filter.

Kind, Regards