This is a long reply… apologies for that but hopefully it is helpful. 
My background so you know where my advice is coming from: I’ve been on Zwift for a few years, have experience with group rides, races, workouts etc. Since Christmas I’ve been working hard to get fit again and lose weight after doing almost no exercise last year with lockdown, and am doing ok at it.
As others have said, leave your trainer difficulty around 50% for now. As you learn more you can play with it if you want but for now it will give you a decent amount of low gears that you can change down into as you ride uphill.
My advice is - you’ve been riding 5-6 weeks and improving your riding and enjoying yourself. This is all good. Time to take the plunge and try and test where you are now in regards to fitness. This might sound scary but it doesn’t have to be. Its about putting a stake in the ground so you can see where you are, and give you something to measure yourself against. I do not recommend you do a FTP test. These are hard to do, especially if you are new to riding, both mentally and physically. I do recommend you do a ramp test. You can select this from inside Zwift, inside the workout menu. Zwift has two different ones depending on how much you weigh. As you are new, even if you don’t fit into the below 60kg recommendation you can probably get away with doing the Ramp Test ‘Lite’ version. These can look scary but you don’t need to worry. You are not expected to ‘complete’ a ramp test. Instead you’ll select the ramp test from the workout menu, I’d put your FTP down as equal to your weight for now, make sure that ‘ERG mode’ is selected in that menu and then hit the ‘ride’ button. ERG mode will control the resistance of your trainer for you so all you need to do is concentrate on pushing the pedals around. You’ll need to stay seated for the duration, no standing up! Even when it gets hard! It’ll start off with some free riding where you can warm your legs up a bit and get yourself to a nice pedal cadence that you enjoy pedalling at. After that ERG mode will engage and the resistance will start being controlled for you. It’ll feel nice and easy at this point. Your job now is to just try and keep seated, and try and keep your pedals turning as long as possible. Every minute the resistance will increase and it will get progressively harder. This is where ramp tests are good because you don’t need as much experience to get something useful from them as you do from a FTP test. You literally just need to keep pedalling until you physically can’t any more. Once you stop pedalling, after a bit, Zwift will realise and move you straight onto the cool down section. And that’s all you need to do. Ramp tests are over quickly, most of it is fine with the last few minutes feeling horrible. But you’ll get through it And practice at ramp tests also helps you do better on your next one so it’s ok for your first one to be not as good.
Importantly doing the ramp test will give you your first FTP value. This is really useful to measure your progress and also to help with all the other things that Zwift does such as workouts, group rides, races etc. It’ll say your FTP value during the ramp test but to be honest you might miss it, if you do, you can always see it in that workout menu that you went into before.
Congratulate yourself for getting through the ramp test! You might want to give your legs a bit of a rest the next day as it can tire them out!
Next I suggest that you try the ‘Zwift 101: Cycling’ training plan. This is a short introduction to how workouts work. Workouts are scaled to your FTP value - so they should be challenging for you, but not so hard that they are impossible. This is why I recommended a ramp test to you - getting a start on understanding your FTP helps so much in other areas. The Zwift 101 workouts are quite short and give you a nice introduction to workouts. It’ll also give you a bit of a taste of some structured rides so you can see how you like it. I recommend that you do the workouts in ERG mode so your trainer takes care of the resistance for you. You want to keep a nice steady rpm value through the entire workout. Try and use your legs to push harder on the pedals rather than just speeding up the pedals.
As I said, knowing your FTP value is your gateway to lots of things.
- Its a measure of your progress. You can do a ramp test in a few weeks time and see how much you’ve improved. And if you are just starting riding like it sounds from your post you should expect quick improvement. Newbie gains are a very real thing!
- Take your FTP value and divide it by your weight in kg. This is your W/kg value. Let’s say your FTP comes out at 100W and your weight is 80kg. 100/80 = 1.25W/kg. i.e. on a really good day, you should be able to ride just under 1.25W/kg for about an hour. Most group rides will advertise what pace in W/kg they expect the ride to be at. So you can use your W/kg to see how you might compare to their advertised pace. Don’t get discouraged by seeing lots of rides at higher W/kg values than you. There are a bunch of slower ones as well. They are there
- If you like the workouts you’ve tried, you could also try a group workout. In a group workout, Zwift will scale the workout to your FTP just like before, but it’ll also make sure that everyone in the group workout stays together on the ride, regardless of their power output. Group workouts are a really good way to ‘workout together’. You may find some chat in the group workout but often it goes quiet when the workouts get harder
Ultimately you’ll get better at riding the more you ride so doing things that are fun and keep you riding is all good. And after a few more weeks of riding and having fun do the ramp test again and see how much you’ve improved!
As I said, they are basically ‘horrible’ for only a minute or a couple of minutes at most which is why they are nicer to do than a full FTP test. You should stay seated on a Ramp Test so don’t be tempted to stand. Ramp Tests are designed for us all to fail at some point so don’t worry about it. Your experience is what is meant to happen.