Personal record for daily steps: rejecting or accepting doesn't work

As a workaround, do it at https://connect.garmin.com/modern/personal-records 

I thought so too, but in the web version in the steps category there is nothing new to accept or reject.

In that case, there is no new record. Just send the record back to the watch (see the button Send to Device, on the PR page) - the records data might got lost or reset during an upgrade, so you need to sync them back.

... seeing the screenshot in the other thread with the PR of 51257 steps in a day, I have a question for you - what is the max daily steps record that Garmin Connect Web shows? 

51 257. And the iOS app forces acceptance of this record, despite the fact that it is a record from the "past", but as I wrote the buttons in the application do not respond.

Did you try clearing the cache of the app, or reinstalling it? You can also simply ignore it - the excess button won't harm anything.

Yes, in fact I have done probably all the things I can do myself. I also installed the app on an iPhone that has never had the app installed before, and after logging into the account (without pairing the watch) it still shows this error.

As far as I remember, the information about the "new" step record appeared simultaneously with some other record „for the longest run”, which I could easily accept.

or maybe it's an elaborate ploy to break this record? ;))) 

Try making a new higher record, perhaps it will then be possible to accept it

:-D