I know there's a lot of hate on lemmy for it, but if you're missing r/fountainpens there's some thriving fountain pen communities on discord that have really helped me get over losing the sub in reddit's fall from ~~grace~~ usability

penposium (Most active, also probably the most ~~misanthropic~~ casual)

r/pens (Most users and a great resource for identifying obscure pens)

pendemic (often do fun group buys and similar)

Stationary Anonymous (General stationary, not just pens)

There's also Fountain Pen Network if you prefer the oldschool forum feeling, though it's much less close-knit of a community than the discords (imo).