Some things to consider:

1. the implementation seems incomplete / too specific. Please search the codebase for example for print_shell or print_self to see relevant occurences.
2. Did you consider using a custom JSONEncoder for datetime (instead of your private function)?
3. Please have a look at the shell output of t.info. JSON format has to reflect all elements there.
4. There is a parser standard option for formats: https://grass.osgeo.org/grass-devel/manuals/parser_standard_options.html#g_opt_f_format (search the code base for: G_OPT_F_FORMAT for inspiration)
5. In the tests please also test that metadata is returned properly (right values) not only the presence of selected keys.

Consider the following (not an implementation!):

from datetime import datetime
from json import dumps, JSONEncoder

import grass.temporal as tgis

tgis.init()

# Create custom JSONEncoder (may go into grass.script ?!? with a different name)
class DateTimeEncoder(JSONEncoder):
        # Override the default method
        def default(self, obj):
            if isinstance(obj, (date, datetime)):
                return obj.isoformat(" ")

# Open an existing STRDS
stds = tgis.open_old_stds("A@PERMANENT", "strds")
# Extract metadata to dict
md = {**stds.base.__dict__.get("D"), **stds.spatial_extent.__dict__.get("D"), **stds.temporal_extent.__dict__.get("D"), **stds.metadata.__dict__.get("D")}

# Print in JSON format
print(dumps(md, indent=4, cls=DateTimeEncoder))
#compare output to output of
stds.print_shell_info()

And please, read again the AI-usage policy! Thought-through PRs are much prefered over super-fast PRs that rely quite a bit on AI generated code...

Hei @sakirr05 . I have been waiting with a review, as I expected some more changes:

1. use of the standard parser option (G_OPT_F_FORMAT) I mentioened earlier,that is still not used
2. my comment about the PR being inncomplete / too specific may have been a bit confusing:

• With too specific I mean, the way you implemented printing of JSON now, would have to be updated for each metadata item that may get added or changed, while e.g. a dict-comprehension would not have to be touched in those cases.
• with incomplete I mean that when you add a method to an AbstractBaseClass, at least my understanding is, that all classes derived from that should implement that method, no? You just added an implementation to a subset... Also it seems you are still missing some metadata keys (e.g. min_min, min_max, ...).

3. The TemporalDataEncoder looks OK, it may be even better to put it in an utils package, as it maybe useful beyond the temporal framework...

I hope others with a better understanding of design pattern in GRASS can chime in (and maybe also relax a bit my requests for changes)...

Much better! Thanks for addressing my earlier comments.
Sorry for not being clear: when I wrote that the JSON decoder class is probebly better served in an "utils" module I actually thought of somethin like grass.script.utils...

@wenzeslaus or @echoix would you agree here? probably even change the name to GRASSJsonEncoder (or similar?

Please also test other STDS types (STVDS, STR3DS) and check again that all keys from shell output are present in JSON...