We develop mobile apps using the tools Xamarin (soon .NET MAUI) and C#, which come from Microsoft, and makes up a very strong and versatile platform. The code is written once but can be deployed to both iPhone and Android phones through their respective app stores. If there is a need for specific adjustments or enhancements on the individual platfom then the tools can also handle that.
To connect the app's with "backend" servers we use REST based services (which we can also develop) and/or the Couchbase database which can synchronise data between server and mobile devices almost instantly. By using this database technology we can also create solutions that work "mobile first" (even though the user isn't online) - and when the user comes online again the data is simply synchronised to the backend server/database again.
Lotus Notes was first introduced in the 1980s, and was then bought by IBM and later HCL software. With HCL, full speed has been regained on development of the platform. Backward compatibility has always been a cornerstone of the platform, so the system you (had) developed 20-25 years ago still runs on the latest server/client!
We maintain solutions that WERE developed 20-25 years ago (client or web-based) and we also develop new solutions - typically in XPages, which is a variant of Java Server Faces (JSF) with Java underneath which knows about the Notes database.
A platform that has and has had an amazingly low cost for many of the systems that customers have had running over decades.
Many years of experience with project management, IT management, development, testing, operation and architecture have given us a good starting point to be a sparring partner in IT projects for customers.
It may be that you just need a half/full day of sparring on a process of choosing a new system for your business. In that process, it may make sense to make a short stop and use an external resource with a different background to yourself - and who may not know your business area at all - to ask the questions that you may forget in the process.
It may also be that you need a resource to help you provide qualified countermeasures to an external software developer who is developing a solution for you. It could, for example, be reviewed at each part delivery during the project.