This from One Mile at a Time.
As quoted in the article, "The Economy Light fare on European routes does not include any free advance seat reservations. You will be allocated a seat automatically when checking in. If you would like to change this seat, an amendment fee starting from EUR 25/CHF 35/USD 35 will be charged with effect from 21.6.2022."
Edit: Lufthansa's previous policy allowed Economy Lite seat selection for free at check in 23 hours before flight (also LH quote from article): "Of course, all the remaining seats can still be selected free of charge once check-in for the relevant flight begins, usually from 23 hours before departure. Please note that, in this case, the selection can in some circumstances be limited."
Note this applies to Lufthansa Economy Lite fares, which are LH's equivalent to Basic Economy:
https://onemileatatime.com/news/lufthansa-economy-light-seat-assignments/