Thanks for your precision!
To the ONT arrives a single fiber with a SC/APC connector, but this is not a problem since I will be using the ONT provided and use the 2,5Gb copper port to connect it to OPNsense (looking for a 2,5 Gb PCI card).
The 2 fiber that I've asked them to run (from OPNsense to server) are terminated with the same SC/APC connectors and I was thinking about using this SC female/female adapter and this SC/APC to LC cable that I've just realized that are still APC...I'll have a look if there are SC/APC to LC/UPC cables
As for that xcvr, please note that it’s an LRM, or Long Range Multimode xcvr. Would it probably work at 30 meters? Probably. But an LR xcvr that is single mode 1310 nm would be ideal.
Is it a LRM? Damn, I didn't realized since I've filtered for single mode. If the filter doesn't work, I've no idea which is LR. Would you be so gentle to point to a cheap one for single mode finer?