Indexing is unlikely to work well mixing Suntour index with a Shimano derailleur, but it should be easy to make friction mode work very well.

Usually this is simply a matter of dialing in the adjustments, including the often misunderstood "B-screw" which sets the height of the RD. Find a tutorial and review it thoroughly disregarding ONLY those relating to trimming the index mode.

However, you're starting out with a handicap because you had a bent derailleur, likely installed on a bent hanger. So you'll need to make sure these are resolved before wasting time trying to adjust. Start by carefully eyeballing the idler cage, and checking with a straight edge, to make sure it's straight and the pulleys are on the same plane with no twist or misalignment between them. Next shift to a gear combination where the idler cage is close to vertical. Place a straight edge (yardstick or broom handle) vertical against the rear wheel, then stand behind the bike and eyeball to see if the cage is parallel to the wheel. You can repeat the same test in the horizontal plane (likely requires a friend to hold things for you), but it's harder to get a well alignd view, so do the best you can.

With the RD reasonably aligned, you should be able to get some semblance of reasonable shifting in friction mode if you follow the tutorial.