You could also consider just running the binary given that alternative fits your usecase? Single-user and trusting the syncthing-team, but they seem (my opinion, no affiliation, fellow user only) highly trustworthy. The binary auto-updates and you don’t have to wait for the distro package maintainers to update the repos. Might be an acceptable tradeoff in the case of syncthing, or maybe not - just raising as an alternative for you to consider.
You could also consider just running the binary given that alternative fits your usecase? Single-user and trusting the syncthing-team, but they seem (my opinion, no affiliation, fellow user only) highly trustworthy. The binary auto-updates and you don’t have to wait for the distro package maintainers to update the repos. Might be an acceptable tradeoff in the case of syncthing, or maybe not - just raising as an alternative for you to consider.