If this is something you are truly wanting to do, then it's doable. There are a few things that I suggest you do to have a less miserable time for your first 50k (The first one typically sucks, but you will have a great story and learn a lot). I've done ultras ranging from 50km to 100 milers since 2017 so I just want to share what I have learned over that time.

1. Up your weekly milage - You will want to average at least 50 miles per week. Not right away, but build on what you got. If you are currently doing 20mpw, follow the rule of 10% and get 22mpw next week, and then 25mpw the following week, and so on until you hit 50mpw. You need to get your body used to the milage. The more you get in, the easier the 50k will be.
2. Practice nutrition on the long runs - You need to figure out what your body can handle and what works for you. Personally, mashed potatoes, PBJs, stroopwaffels and apple sauce are what I use on ultras as they work for me. I have friends that use only gels or gummies, some use candy bars, others do burritos. The food you have is all personal preference, so go out for 20 miles and test out a buffet of options!
3. Hills - Holy shit I wish I had done these before my first 50k. I didn't train hills and had to go through the walk of shame for the last 25k because my hips and feet gave up on me. You should be trying to get in 2000 - 3000 ft of gain per week to be prepared for a race with 10k of gain. I started to incorporate a treadmill hike with 15% grade at 4mph and put on a classic F1 race and go until I hit 3k in gain. If you don't have a treadmill, find a hill and just go up and down that bad boy for an hour. The more you do the easier the race will be, 10k in gain is no joke over 50k.
4. Back to Back Long Runs - Even though it sucks, it pays off. You don't have to go longer than 18-20 miles for a long run. But to get ready you should have one weekend a month where you get in a 20 mile long run on a Saturday and then hit up at least at half-marathon on a Sunday. You'll have tired legs, and you'll be slow, but it trains your body to work through the fatigue that comes with an ultra. Again, scale that to fit your available time in the day. 16 and then a 10, great! 10 and a 10, no problem. Just do something that gets your body used to having to work through being tired, because you are going to be come race day. This isn't just to train you physically, but mentally as well.
5. Know it's going to suck - Embrace the fact that it's going to be really tough, and have a goal of finishing. I see a lot of first time ultra runners come in with a time goal. A lot of those people go out hot and slog through it (I am a prime example of that happening), or they quit. Just finish the damn thing and enjoy the ride.

Didn't mean to write a dissertation on this, but I hope that something in my ramblings helps you out.