Here's how we digitize our administration in Germany the proper, Germanic way:
A fixed sum for digitization is allocated and the local government publicly advertises a project. A bureaucrat higher up the foodchain has a friend/cousin/former colleague who runs an IT service business side gig. Guess who will win the contract. The friend/cousin/former colleague starts building by outsourcing the project to some sweatshop. The project will exceed its initially planned costs and timeline by a factor of two or more. Once completed, the final product will consist of a clunky frontend allowing the user to fill a form. After the user has completed the form, it will be distributed via e-mail to the low-level clerks. They will print it out and process it by typing the very same information into another software running on their work computers. Print again. Then the user has to schedule an appointment at the local administrative office to get the form signed and stamped in person. Upon completion, the finalized form will be faxed to the next administrative authority in the chain.
The frontend runs on a Raspberry Pi located somewhere in the administrative building. That server will of course be turned off when all administrators have left the building (save energy!), meaning the frontend will only be available during weekdays from 8 am to 1 pm.
But. I have used Elster and, while it is true it looks old and overly complicated, it actually works great.
You get _a lot_ of very useful warnings about fields that cannot be 0 or must at least be x, based on some other distant field. You can save previous forms and start from them (for recurrent things like VAT quarterly declaration). You can save progress and log in using certificates, change to be notified electronically instead of per physical mail.
IMO Elster would be even better if they would _never_ change the number of the fields. If you buy a book about German taxes (I know, fun) they can say fill in field 47, and it it prob now 49 because the fields changed.
I did them in Spain. Honestly German taxes were a bit more intimidating (so many fields, tk is different) but in the end you only need a few. As a salaried employee you can use taxfix and get it done in 20 min.
In Spain they were easier, but also I could not expense many things as a contractor. In Spain they would send you a draft, and you can request a meeting to help you do them (few people do this). This was smooth. You show at your timeslot and a friendly person is there for any questions. Before you leave, the definitive version is done.