My son (who lives with me) and I both had an undiagnosed virus in March, which had all the symptoms of covid, but "couldn't possibly be because there is none here". We were not tooo sick and just took paracetemol and rested. For both of us the symptoms persisted for quite a while - even now I have some but he is much improved. Both of us had sore big toes and the nails on both of our toes cracked. They are currently growing out and will repair themselves, no doubt. My son does have psoriasis and he was pretty sure it was an effect he had read about in which psoriasis develops this kind of effect. I never had psoriasis before, but maybe it was latent - my father certainly had it.