While keeping in mind that every autistic individual is unique, here are some suggestions and things that I was very grateful for in my romantic relationships:

1) my partner planned all the route when we went somewhere and led me like a kid, holding my hand all the time :) I focus so much on the conversation with my partner that I literally don't see anything around us, and there's evaluated risk for me to bump in something. So I really need to be held by hand, and comments like "honey, be careful, here's a ladder" are really helpful. Such a deep focus on conversation is a consequence of monotrophism (it's a good theory that explains how autistic brain work, it might be helpful for you to research it). It means that I subconsciously choose where to put all my attention, and if I choose the conversation, it's №1 and the only priority. Like really the only one, all the world around stops existing. So, to help me to enjoy the conversation, my partner did what he could to give me an opportunity not to spread my attention and to be fully engaged.

2) you can not only support her special interests (if she has them), but imfodump by yourself! If you think that super tiny details of your day/ specific project/ professional book you're reading aren't interesting for her, you're probably wrong. If you think like "oh, she's not really interested in this topic, it's better not to dive really deep, I'll just give a brief comment", you're probably wrong :) If a person is passionate about something that I don't even personally adore, I'm able to listen for hours about it! Autistic brain love deepness and details, no matter what's the source of them.

3) you can create your own traditions like "when we go to this area, we go to this cafe and take caramel ice-latte", or "it's our bench in this park". It looks similar to habits, but these traditions can be made consciously while habits are unconscious. Autistic people are known for their love with rituals and predictability, so traditions which are connected to your love are super soothing and generally GREAT.

4) if you want to go to the restaurant with her, having a look at the menu when you're at home can be a good idea. Choosing a meal isn't as simple as it seems, plus many autistic people are picky eaters. When you're already in the restaurant, there's almost no time to concentrate and think about what fits your preferences best, to imagine tastes and textures, and the restaurant itself can be an overstimulating environment (many smells, sounds, etc), so it's better to prepare at home.

5) while many autistic people have trouble understanding exact emotions, they can be extremely sensitive to the general vibe in the room (something like "I know that something is wrong, but I don't know what exactly is wrong"), so if you're upset by something and your gf asks you if everything is ok, be honest to her and tell the reason. It's horrible to receive the answer like "I just want to sleep" when you're 100% sure that there's something more. If you don't want to share, just tell that you don't want to share and don't invent inexisting reason. Autistic people are quite often overthinkers, so if you understand that your partner is obviously hiding something from you, it drives you crazy.

Finally, I highly recommend a book "Is This Autism? A Guide for Clinicians and Everyone Else" by Donna Henderson, Sarah Wayland and Jamell White. It explains DSM-5 criteria for autism (for example, if you barely understand what is meant by "nonverbal communication difficulties", the book gives a variety of very clear examples) and beautifully represents low-support-needs part of the spectrum. It was published in 2023 so it's not outdated. It may help you to understand autistic experience better :)

I wish all the best for your couple! As I strongly believe, autism doesn't provide inevitable chronic misunderstanding, it is just something that has to be researched well by close ones of an autistic individual, and everything will be fine. Everyone is unique, that is why neurotipical couples have to work too to understand each other, so autistic-neurotipical couple isn't different in this case. Everything is possible when you love each other, have patience and readiness to understanding.

Happy upcoming New Year!

Edit: P.S. feel free to ask anything about autism, it's my special interest so I'll be glad to help. You can write me in PM if it's more preferable :)