Problem with release upgrade from 20.04 to 22.04

I have an Intel NUC7I3BNK running on Ubuntu 18.04 perfectly since 7 years. Now wanted to update to 20.04 what was successful, the systems runs stable all fine. However, I wanted to go up to release 22.04 and this failed. I get the error below.

xxx@yyy:~$ sudo do-release-upgrade -d
Neue Veröffentlichungen von Ubuntu werden gesucht
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xe4 in position 3: invalid continuation byte
The above exception was the direct cause of the following exception:
SystemError: <class 'UnicodeDecodeError'> returned a result with an error set
The above exception was the direct cause of the following exception:
SystemError: <class 'UnicodeDecodeError'> returned a result with an error set
The above exception was the direct cause of the following exception:
SystemError: <class 'UnicodeDecodeError'> returned a result with an error set
The above exception was the direct cause of the following exception:
SystemError: <class 'UnicodeDecodeError'> returned a result with an error set
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
  File "/usr/bin/do-release-upgrade", line 133, in <module>
    m = MetaReleaseCore(useDevelopmentRelease=options.devel_release,
  File "/usr/lib/python3/dist-packages/UpdateManager/Core/MetaRelease.py", line 100, in __init__
    cache = apt.Cache()
  File "/usr/lib/python3/dist-packages/apt/cache.py", line 170, in __init__
    self.open(progress)
  File "/usr/lib/python3/dist-packages/apt/cache.py", line 232, in open
    self._cache = apt_pkg.Cache(progress)
SystemError: <class 'apt_pkg.Cache'> returned a result with an error set

I had the "UnicodeDecodeError" also when I was upgrading to 20.04. But the upgrade went through and everything was fine. But the one to 22.04 did not start, but failed. I went already through a lot of forum entries, but could not find anything that helped. Someone has an idea?

Thanks for the support in advance, Matthias