I also blocked on “Hello” frequently and would revert to “Yes” which sounds super corny and over the top or there’s the “Good Morning” or “Good Afternoon” line; all less than stellar options but you know how it goes. I read a lot of thesaurus in my life and ended up saying tons of ridiculous shit in place of what I wanted to say. I totally feel for you and hope you can come up with workable solutions to maintain fluency. Hang in there, it has gotten more manageable as I have gotten older.