Tubi is pretty good.
https://tubitv.com/
I do an amount of watching youtube on my roku tv which actually surprises me. Lots of history stuff and whatnot.
Rumble also has a roku app.
And I listen to a lot of podcasts on the Spotify roku app.
Filmrise is another free movie app. and it has apps for particular genre too, such as scifi, western, mystery etc. in case you have a specific interest and dont want to spend the time sorting through the entire catalog.
That hopefully helps as a general selection to try out. See which kind of thing you prefer and then build your own library of apps on your roku from there.
P.S.: All the above are free with no manditory sign up fees. Spotify has a paid version but you get a lot from the free account.
Cool. I got Filmrise added and I also programmed in my Rumble account. I already had Tubi. Thank you!