Haven't you noticed the decline in support for Ukraine in the West since the counter-offensive didn't go according to plan? Or has the taste of disappointment already washed off Zelensky’s lips at the results of the NATO summit in Vilnius, which left Ukraine in limbo by canceling the NATO membership plan and offering no clear entry algorithm in return?

No, I haven't noticed decline of support after watching some last military aid packages that were announced already after NATO summit. Results of NATO summit, maybe there was high expectations about it, but it ended more or less like I expected without making important decisions.
Perhaps sanctions do not work well if Putin manages to finance the European opposition.

Russia always will find money to fund war machine, propaganda and opposition parties in West. And sanctions - IMO, it's joke. It would work if it would be imposed like supposed. But when it's bypased using parallel import/export through countries like Turkey, Kazkahstan or Armenia, offcourse it doesn't have as much effect as expected.