Troubleshooting

The device won't boot at all (black screen)

The card is exFAT, not FAT32. LodorOS mounts the data card as vfat; an exFAT card silently fails and the device falls back to stock. Reformat FAT32 and re-extract.
The filesystem is dirty. A card that used to boot but suddenly won't often has a corrupted FAT (e.g. from a forced unmount). Run diskutil repairVolume (macOS) / fsck.vfat -a (Linux) — the data is usually intact, only the FAT bookkeeping is broken.
You dragged the files instead of unzipping. A Finder/Explorer drag can skip the hidden .system / .tmp_update folders. Re-extract with a real unzip -o.
(H700 only) TF1 isn't in slot 1, or the data card isn't in slot 2. The H700 boots from the TF1 card, which chainloads the LodorOS data card in the second slot.

The volume label doesn't matter — you don't need to name the card anything specific.

Tailscale, on a fresh card: a fresh install has no saved Tailscale login — you must sign in again (new QR). It doesn't carry over from another card.
Using the 100.x IP for Tailscale: don't — tailscale serve routes by hostname, so enter the *.ts.net name.
Cloudflare Access getting an HTML login page instead of data: the Access policy action must be Service Auth (not "Allow"), and the app should be set to return 401 on token failure. See server setup.
"Couldn't reach RomM": confirm the address form matches your transport — *.ts.net for Tailscale, the public https:// host for Cloudflare, or the LAN IP:port for home network.

BIOS-dependent system (Dreamcast, etc.): you haven't supplied the BIOS. LodorOS is BYOB.
H700 heavy system (N64/DC/PSP): these run the stock Anbernic RetroArch; if your device's stock firmware is missing that core, the system is skipped. Make sure your TF1 stock card is present.

Confirm the device actually paired (a RomM client token is stored) — an unpaired device reaches RomM but gets 403 and can't sync.
Saves pull before a game and push after you quit. Give the push a moment on exit before powering off.
You can restore an older save from the server via the per-game menu.

Eject cleanly (diskutil eject). Do not force-unmount — that's the #1 cause of a card that then won't boot.
If macOS Spotlight blocks the eject, mdutil -i off /Volumes/<card> then retry the plain eject; don't force it.
After extracting, dot_clean the card to remove ._ junk.