Git-based SaaS has weak lock-in, unless you waded too deep into platform-specific integrations. Agile-oriented project management, while it tries to have platform specific ways of grouping, labeling, etc. is also weakly sticky because task descriptions are (or should be) what matters.

This is good, especially for small new teams at startups that want to shop different tools before having a lot of stuff to move around.

All SaaS aspires to be sticky because investors told them to be that way. Almost all SaaS with institutional investors has to make stickiness noises. But it is easier for some than others.

I the SaaS is Open Source, you can always host it yourself, or pay some one else to host it, or fork it, or any number of other solutions if the current provider does not fit anymore. Open Source is the best way to fight vendor lock-in.

If not Open Source, it should use open standard APIs and data models, with free or cheap data export.