Can someone be a cleric without following a god? Like maybe instead following an ideology or even draw power from one of more planes of existence (ex. Positive energy plane or plane of fire).
aye… on Athas (Dark Sun) there were Templars who worshipped the dragon kings, and Clerics who instead forged an allegiance to one of the elemental planes, as well as Druids who simply serve the spirits of nature. it introduced the idea of Preservers and Defilers (on the mage side) who drew magical energy from the lifeforce of the local plant life - preservers pulled small amounts to merely weaken the natural order, defilers just RIPPED everything away, leaving only dead ash in their wake.
in 10e, being an unaligned priest or cleric largely means you serve a subsect of deific and planar powers - so, for example, Druids can follow their race-specific god or just continue to serve nature itself, pulling tiny bits of magic from ALL the nature gods. Elemental clerics work in similar fashion - drawing their magic from their respective elemental plane as well as the lifeforms all around with minute connections to it.
one thing to keep in mind, however - being an unaligned cleric GENERALLY means you won’t get taxed with tithes but ALSO that you won’t be able to call upon allies from your church. that might not mean much at our current level, but in low level games its a serious hindrance… having access to healing/resurrection/etc at cost is hard to sneeze at