hmm - been a while - but Paul used to load external icons (for weather) like this - https://flows.nodered.org/flow/d65756991da6df708400b9d9819ed9b7 - we stopped having to do this when he created a nice subset that was small enough to load all the time).
I then added support for icofont (https://icofont.com/ ) fonts that could be loaded via a template in a similar manner but if loaded in the head could then be used more widely within dashboard by using icofont- as a prefx (like fa- fonts are). So you can go to their site and create your own collection of icons to load.
[{"id":"f8da13db.bf715","type":"ui_template","z":"c4f68fc3.2dd88","group":"68d7ee81.54ea9","name":"","order":0,"width":0,"height":0,"format":"<link rel=\"stylesheet\" href=\"/icofont.css\">","storeOutMessages":true,"fwdInMessages":true,"templateScope":"global","x":300,"y":300,"wires":[[]]},{"id":"df12003.e1dbe","type":"ui_button","z":"c4f68fc3.2dd88","name":"","group":"68d7ee81.54ea9","order":1,"width":"5","height":"2","passthru":false,"label":"Washing machine","tooltip":"","color":"","bgcolor":"","icon":"icofont-washing-machine icofont-2x","payload":"","payloadType":"str","topic":"","x":370,"y":360,"wires":[[]]},{"id":"68d7ee81.54ea9","type":"ui_group","z":"","name":"Examples","tab":"4301b423.548afc","order":1,"disp":true,"width":"12","collapse":false},{"id":"4301b423.548afc","type":"ui_tab","z":"c4f68fc3.2dd88","name":"Test","icon":"school","order":4,"disabled":false,"hidden":false}]
