Well ankermann only give a 2 year warranty which is very average.
Had a play about with their build configurator... Can't say the prices and options are the best available, but the example build options I mentioned previously are possible to fit in the budget... (With a slightly better choice/freedom of component selection this could be tweaked better but can only go with what's offered):
Assemble your own desktop PC now ▷ Fast and inexpensive with our PC configurator ⭐ Guaranteed compatibility ✅ incl. 2-year guarantee ✅ | ANKERMANN
www.ankermann.com
This build forgoes a GPU now but offers modern upgradable platform - easily accomodating mid range future GPU upgrade in short term, and a future CPU + RAM upgrade longer term. Again, this goes with the premise of the games/software you intended to use. If you've suddenly decided Cyberpunk 2077 is for you then you'll need a GPU option...
Spending a tiny bit more on the PSU (going to the Corsair RM850 would be worthwhile but nudges above 800) and upgrading the RAM to 32GB DDR5-6000 would be worthwhile changes if they are affordable.
But, I still think you can do better... There is likely a better configuration somewhere at a retailer available to you.
If you mean actually properly buy parts and build it yourself, you can definitely get better value for money - that last media mart PC is least good option in terms of features and value - the other options in your post are better in both performance and relative value in that sense.