I seldom see nice design in ERP or enterprise level system. Maybe I haven't seen much.
Software companies in my country only use whatever available in the market. Usually the default controls available in Visual Studio. Look ugly but it sells. Some will invest a bit on third party controls like Syncfusion. That's all. Nothing fancy or creative.
Google Material Design focused on simplified and clean design. I don't think it is good but at the same time not bad.
iOS native design also plain and clean.
After years of using B4A, I already used to abstract designer. If I want to see real preview, I have it on my real device through bridge or emulator. That is true WYSIWYG view. For me, B4X suite is a RAD tool as it claimed. It also
save resources not to load complex preview in the IDE. This is great for older or less powerful machine. B4A/B4i/B4J also provide actual user experience in Debug mode. All these reasons answer to why I prefer B4A than Android Studio or Visual Studio.
I think nowadays Low/No Code tools are getting popular in enterprise. Again, I expect the controls also offer not much of choices.
Many developers here provide a lot of custom libraries which are super beautiful. Even the default views or internal libraries can be highly customized to look good in different style or themes. In my opinion, B4A/B4J are better than many paid or subscription based tools like xojo.
Therefore, I advise you to contact the Cogniteq company, which is developing flutter
https://www.cogniteq.com/flutter-app-development. This helped me finish my started projects, which I could not finish due to lack of knowledge.
I haven't seen your POS. I admit I am not a good UI designer. For me, I am satisfied with the POS I developed with B4X. I can say much better in term of design compare to some of the popular POS in my country. Design is only one of the selling points but there are other points that make a system sells. Perhaps, pay or hire someone who can design better UI.