Are celebrities still relevant? Don't know, I personally would have never cared. But it seems as though they overdid it so much this time that probably nobody is going to pay attention.
I believe the issue here largely is about more serious matters like income and peace, which Trump finally realized is a good idea to bring to the forefront. Ironically Trump even realized the Muslim vote could play a deciding factor and brought some Muslim figures on stage to endorse him. Them saying Trump is going to bring peace to the middle east is just make believe, but with Kamala being the war monger that she is, expectations are high on Trump. At this point I'd be surprised if he loses unless something terrible happens.
Yes celebrity endorsement still relevant, They can get a lot of support since those famous personalities have huge following and lots of them would follow what those famous celebrities says. But that's not automatically could give them a win. Since for sure there are lots of thinking voters that those shows made by celebrities is just endorsement which they are benefiting.
Now both candidates do all what they can to attract lots of voters November is about to come on next few days that's why expect that maybe they do more aggressive campaigning since to possibly get more votes and sympathy from their target people.