The only non-trivial bits are things like capital gains, work expenses, donations, but these are all things that you should be tracking in a spreadsheet as they occur through the year, and you'll have a number at the bottom of that spreadsheet that you can just copy over to your return (like I did with my capital gains, for example).
Even as a contractor in the past (keep in mind, in Australia, a contractor is a sole proprietor business), filing my return was as easy as copying income/expense totals from my invoice/receipt tracking spreadsheets into the return, adding any new depreciating assets to the list (that persists on their servers and gets recalculated each year) and submitting.
I don't have any interest accounts or private health insurance, but these would be some of the other things that get automatically pre-filled. And it's been this way for well over a decade now.
The only thing you have to worry about is the end of year form. What you submit is usually a good first suggestion and the german IRS equivalent will send back a proposal. If you don't do anything, that's what they collect.
Of course, the tax forms in germany are rather... complicated, there is a lot of pitfalls, though generally unless nobody at the IRS spots it either, you'll get a correction back.
Austrian tax returns are much simpler because in the majority of cases they don't exist: Your employer and your banks automatically withhold the correct amount of taxes (capital gains are taxed at a flat rate and don't influence regular income taxes). Marriage status doesn't matter for income tax as the same tax brackets apply to everyone. Deductions are much less common but if you have any deductions you can let the government know and they'll automatically refund your tax within a week or so.
One reason why Austrian taxes are so much simpler is because there are much fewer special cases: The US has all those different credits and deductions that lower the taxes in certain situations, e.g., the "First-time homebuyer credit repayment". Meanwhile in Austria all those subsidies for, e.g., lower income people aren't included in the tax system, but are available via completely separate programs (e.g., if your income is very low the government pays parts of your rent and helps you with heating costs in the winter, but you have to submit a separate application for that).
Not sure which system is better. One thing I noticed is that in Austria I never applied for any subsidies even while being a low-income student (why would I apply for social services if I don't really need them?). Meanwhile in the US my tax advisor makes sure that I get all the credits and deductions that I'm eligible for.