calling

MRID=$(gitlab -o json project-commit merge-requests --project-id ${id} --id ${COMMIT_ID})

with
COMMIT_ID 2fdd3e323446d24ca80e36e41aa710a853662fac
and id = 63

(valid and working via curl call)

give as output

Traceback (most recent call last):
File "/usr/local/bin/gitlab", line 8, in
sys.exit(main())
File "/usr/local/lib/python3.9/site-packages/gitlab/cli.py", line 377, in main
gitlab.v4.cli.run(
File "/usr/local/lib/python3.9/site-packages/gitlab/v4/cli.py", line 549, in run
printer.display_list(data, fields, verbose=verbose)
File "/usr/local/lib/python3.9/site-packages/gitlab/v4/cli.py", line 415, in display_list
print(json.dumps([get_dict(obj, fields) for obj in data]))
File "/usr/local/lib/python3.9/site-packages/gitlab/v4/cli.py", line 415, in
print(json.dumps([get_dict(obj, fields) for obj in data]))
File "/usr/local/lib/python3.9/site-packages/gitlab/v4/cli.py", line 397, in get_dict
return obj.attributes
AttributeError: 'dict' object has no attribute 'attributes'