For some (strange) reason, you have an old updater - 2.6.25.40 which does not see newer versions of DCS.
Please, replace your updater with the one from https://updates.digitalcombatsimulator.com/
Interestingly enough, you managed to update to 2.5.3.22877 using fresh updater.
After that it got magically replaced with the old one...
Do you have any AV software installed?