The SeatDefaults section, as expected, set the default values. However, once a user has already logged, the session they used (even if it was the default left unchanged) is taken as their session choice. So changes to SeatDefaults no longer apply to them. They'll have to manually select the session from the menu next to their username (usually a gear icon).
De mondjuk csak bejegyzi valahova, szoval fognam es grepelnek egyet a cinamonn-ra a conf.d-ben (vagy xsession, vagy .config vagy .local)
"lightdm --show-config" mit mond?