Alba is not big, still very new and has not had a single candidate elected yet. All its elected members have defected from the SNP.
But they have played this cleverly by making an offer to Yousaf that he wouldn't accept. Now they look to disgruntled SNP supporters like the ones who are serious about independence. And to less disgruntled SNP supporters, well it was the Greens who brought Yousaf down, not Alba.
There won't be a Scottish election until 2026 now, so they'll be hoping they can build enough support to get over the 8% mark where parties start picking up list seats. Until now they've been polling only about 2%.