My knee hurts a little and my left index finger get numb, and I miss seating in a position which makes me feel I want to make more effort

I’ve got a pretty similar style of bicycle to yours. These omafiets-style/upright/commuter bicycles tend to prioritize comfort over speed, so a few things might need changing.

As @[email protected] mentioned, your handlebar is a bit low. I’m assuming it was lowered to achieve a more sporty position? If so, I would suggest trying out flat handlebars if you can - the current “swept” handlebars fitted to the bike aren’t really ideal if you’re after more agile/sporty handling.

Since your body is currently going to be leaning slightly forward rather than completely upright, I think that big seat might get a little uncomfortable on long rides. Something narrower may be more ideal - however I would strongly suggest a bike fit if you can, since they’ll be able to advise correctly here.

Is that an internal hub at the rear? These do change how the bike feels to pedal, so I’d suggest trying out a bike that has a derailleur and see if it’s something you’re particularly bothered about. It looks like a three speed to me - which might be quite limiting depending on your fitness level and amount of hills etc. I have a 7 speed Nexus personally and I find it plenty fast, however IMO the resistance makes the bicycle feel a bit sluggish sometimes

You could also look at running the tyres at a higher pressure for smoother rolling, at the expense of grippiness/traction, and ride comfort. Mine are 40mm wide and I run them at 85psi (~5.5bar).

My main recommendation though would be to either get a bike fit so they can get you set up all nicely, or perhaps look at getting a second hand “sporty” bike with most of these considerations already taken into account

Edit: replace bakfiets with omafiets