Gaia GPS is fantastic. You can mix and match layers, and specify what bounds you want to download for a trip.
Right now I've got 3 GB stored locally, some of that for the usual locations that I wander out of connectivity, and some for a trip next week.
Garmin (formerly Delorme) Earthmate despite their other issues is great for state or province wide vector maps. Not as great for fine navigation and tracking (as it's designed to be paired with and control an InReach), but good for point of interest exploration.
I love Gaia on my iPhone and iPad, but I’ve had real problems with map layers not displaying lately. MapBox Streets and Gaia Streets are both hosed and I can’t figure out why.
Forgive the potential facetiousness of my reply because I know it's not exactly what you're asking for, but if you know where you'll be then save the images somehow. Knowing how flakey Apple Maps is without connectivity, if it's important, then I'll take screenshots of the route before I leave, for the same reason I'll print out important slides of a presentation because even a lo-fi plan B is better than total failure.
Are online maps really that much better than a paper map? The only real improvement is the same as that of mp3 over carrying a walkman and bunch of tapes. There's not much beyond that, for all the hype.
Like so many things (Amp/SPA websites; social media; 24 hour rolling news…) they seem to me to not really improvements over what we had, because someone somewhere tried to lock the customer in. Maybe that's just misanthropic luddite me.
Typical satnav devices work fine without internet connectivity. Of course, such a device won't work if it can't connect to satellites providing positioning data but I think that was not what you had in mind when you said "connectivity".
Trailforks is power hungry but is great if you're on-trail. If you're off trail, hilariously Garmin Explore I think is pretty good, you can download Topo and USGS maps, but logging in isn't working right now :) so look elsewhere
Here Maps for vehicle nav. If you download the maps of course. OSMAnd and Windy Maps w/ on device maps for outdoor. Here is also used on Audi's satnav I think. The voice is the same and the missing roads are the same.
