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.
The UK tax return (AKA Self-Assessment) follows this pattern and it definitely makes it better. It still lacks clear explanations of every field though.
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.