Yes, You can get Turn-by-Turn with offline/downloaded Google maps. We use this in the mountains.
But, I would NOT assume that Google Maps "forgets" your previous mappings when offline. I assume whenever I reconnect, Google download stored history then run statistical algorithms to figure out who I am from city, neighborhood, home location, frequented places, etc... Google has directly available location data from what you are doing, then they can easily run "Big Data" (this case is actually quite easy) statistical algorithms on everything they see.
How many Google Map "devices" pull into my garage? How many cars pull into my garage, then drive to my in-laws house, then stop at our favorite happy hour spot, then drive to our favorite grocery store parking in roughly the same location in the parking lot? You are statistically identified very very easily.
These are my assumptions whenever using any Google apps (Maps, Gmail, Adsense, etc).
Having said all this, I have two "polluted" profiles - one for work since we use G-Suite and one for personal (Gmail, Whatsap, Seatgeek,etc) - that I always shutdown when not active. I spend as much time as possible in FOSS only profiles on my GrapheneOS device.