I defy anyone, including, the OP to say they have never permitted themselves to treat themselves to a self indulgent waste of money at some time in their lives. It doesn't have to be beauty treatments, it could be an extra cup of coffee, a favourite food, a packet of seeds.
When it comes to beauty treatments, I am among those who do not particularly enjoy massages, but DH, DD and I love a day at a spa, one of those which is a water playground with indoor pools, outdoor pools, jacuzzis, different hot and cold showers heat rooms, saunas. We have no interest in any other facilities they may have. Actually that is a good idea, why do we not celebrate the end of lockdown with a spa day at our favourite spa?
I am looking forward to a haircut and getting my brows shaped and tinted, but that is just normal self maintenance contracted out.
There is no virtue in never having beauty treatments. but perhaps a bit of virute signalling, which, of course, is also a self indulgence.