Set up a "global" ignore file that gets synced between devices. Call it .stignoreglobal for example and and change the .stignore file (which doesnt get synced) on every device to only include #include .stignoreglobal. Now your ignore state gets synced between devices and you can make changes from anywhere.

Mine looks like this:

// Incomplete Downloads
*.part
*.crdownload

// OS-generated files
desktop.ini
Thumbs.db

// Cache
cache
spotifycache

// Unity analytics
Unity

// LineageOS updater
org.lineageos.updater

// No read access :(
/Android/{data,obb}

You can learn how to write one yourself here: https://docs.syncthing.net/users/ignoring.html

Other stuff:

• On Android I use this: https://f-droid.org/packages/com.github.catfriend1.syncthingandroid/
• Some Info on how you can reduce battery usage: https://github.com/Catfriend1/syncthing-android/blob/main/wiki/Info-on-battery-optimization-and-settings-affecting-battery-usage.md
• Make sure SyncThing is excluded from your phone's battery optimizations (varies by vendor).
• To save on mobile bandwidth I have it set up to only sync on WiFi.
• You can set up a symmetric key (basically a password) and sync your stuff to a friends instance. Your friend will not be able to read the data without the key (make sure it's a long random string). This also helps if you're running a SyncThing instance on a VPS for example.