As far as I am aware of, according to Mills rather than H2O on its own, it's the process that chemically forms H2O which is a hydrino catalyst (in the presence of hydrogen atoms), i.e. "nascent water".
Right in the claim of the application I linked earlier: https://patents.google.com/patent/US20200002828A1/
1. A method comprising:
a) producing a voltage differential between a set of electrodes separated to form an open circuit;
b) injecting a conductive material between said electrodes to close said open circuit;
wherein said conductive material comprises reactants capable of forming nascent H2O and atomic hydrogen; and wherein the current and voltage in said closed circuit is capable of initiating a plasma forming reaction;
c) collecting the products of said plasma forming reaction;
d) regenerating said conductive material and/or one or more of said reactants from said collected products; and
e) loading said regenerated conductive material and/or one or more of said reactants between said electrodes.
However, I don't know how this could be related to Holmlid's research.
In the past it was shown by Holmlid et al. that styrene catalysts can form Rydberg K–OH2 (alkali–water) complexes, but I haven't found suggestions that these can also form Rydberg matter (or in other words, a phase composed of just these complexes): https://doi.org/10.1021/la034142t
If RM could be formed from them, incorporation of other atoms and molecules could be possible similarly to how it occurs with alkali RM, but I'm not sure if this is much related with Alan's report above which seemed to only involve atomic hydrogen and water vapor.