What solutions exist to store data in text files and future-proof against tampering?
In addition to good recommendations on the InfoSec SE site, some of which are not that difficult to implement (for example, digital signing), I would suggest another rather straightforward solution (unless your data is extremely large or extremely sensitive): simply use one of Git repositories, such as GitHub or GitLab, or research data repositories, such as Zenodo or figshare.

Git and Git-based services now support large files, plus you will have an added benefit of versioning for data files that you can match with your research workflows to enable reproducibility.

Check my related answer on some arguments for potential preference for Zenodo vs. figshare.