I pot my Pelagonium geraniums in soiless mix. I have taken cuttings for years and I tried many methods but this is the best. This is how I do it--taken from my plant file

TAKING GERANIUM CUTTINGS

First you must make sure everything you use is very clean.

Take your cuttings: With a sharp knife or razor blade cut a 4 or 5 inch
piece from the growing tip, cutting just below a leaf. All roots and branches
come from a leaf joint. Remove all but the top 3 or 4 leaves. Let your cuttings
callus over--Lay them out somewhere on newspaper. Mine sit on my spare room
floor. Let them sit for about 3 days or so. The leaves will look wilted and dead but
they're not. The cut end will shrivel and dry. Letting them callus over and
watching the water cuts down on blackleg a deadly fungal disease especially to
cuttings.

Now plant your cuttings. In a clean pail mix your soil with the water so you
make sure the soil is damp right through. Use a soiless mix like pro mix or
one that is formulated for seeds and cuttings. Just make sure it has no
fertilizer in it. You want the soil wet but not too wet. Squeeze a handful and
some moisture should come out but not a lot. Fill your pots and make a little
hole in the center with your finger or something else that will make a small
hole.

Dip about 1/2 inch of the cut end in rooting hormone. It comes in powder or
gel, either is OK as long as it's for soft wood cuttings. I use Stim-root NO.
1. After it's dipped put it in the hole and cover it in, and you're done.

Keep the soil moist but not overly wet and make sure they have enough light--Mine go under grow lights with a humidity dome. They will look wilted at first but
that will change as it starts to grow roots. You will know it's rooted when it
starts to show new growth. If you are going to plant it outside, wait until it
is rooted well before you set it out.

Using this method I still lost some but it did cut down on the losses. A few years ago I decided to use a heat mat under my cuttings and it worked wonderfully well. I only lost 1. Now I do it all the time with great sucess. When new growth starts to show remove them from the heat mat

I just transplanted my rooted geranium cuttings from 6 pack tray inserts into pots. I started 26 cuttings using my method and I transplanted 23 rooted plants into pots and there are still 2 iffy ones that haven't yet showed new growth. The above method works better than any way I've tried in the past and I think over the years I've tried every way there is to try and produce plants from cuttings. It doesn't matter the variety. They all root.

Trying to root in water was hit and miss--mostly miss.

Rooting in soiless mix with rooting hormone was a bit better

rooting with hormone powder after letting them callus over was much better but I still lost too many

Using the above and adding a heat mat turned out to be the best move with very few lost plants

Last year I had some jiffy pellets I wanted to get rid of. I'm not the biggest fan of jiffy pellets but that's another story. I soaked them to retain water and then peeled off the outside fabric (otherwise it chokes the roots). and put a cutting into each. Next I put a capillary mat in the bottom of a seedling tray, placed the pellets directly on the mat, and added a bottom heating mat underneath the tray (no humidity dome). This had 100% success for me within 2 weeks (faster than my fancy aeroponic cloner) and the advantage of seeing the roots poke out of the pellets once they had taken. Only tried it once but this is now my go to method for pelargoniums.