Digging holes to concrete fence posts

Mix the concrete as firm as possible, pour it into the hole, insert the sleeves and align them with the spirit level. Do not touch it again until it is somewhat dry.

That's exactly what I wanted to write. In firm concrete, they shouldn't move on their own anymore. Beforehand, stretch a string so that all sleeves are nicely aligned.

I would still attach them to a wooden structure with clamps. However, I can imagine preparing a fence panel with 2 posts ready and then trying to concretize them completely. If I insert the sleeves without anything, I still fear they will shift.

If you work really extremely cleanly, it probably works with washers, etc., but if you just add 1.5mm underneath, that is already quite a lot of deviation at a height of 1m.

He writes:

To me that sounds complicated and like it requires many hands.

Can't you return the sleeves?
Especially as a lone fighter, my method sounds easier. Maybe less durable, I don't know, but definitely easier to handle.

As I said, just under 60m from Friday noon until Saturday evening with three people. The fence posts are 1.6m long and are concreted in 50-55cm deep.

Doing something like that alone is of course shit anyway.

Emotionally, I would rather stick with the sleeves than use fasteners that are anchored into a concrete foundation.

Dig holes, pour in damp concrete, drive sleeves in directly, insert fence posts, align the posts with string and spirit level. Let cure for one week, mount fence panels. If you only align the sleeves, it will be crooked, sleeves are not straight and angled.