I found about the Grail/Galleri test 1.5 years ago from another pancreatic cancer patient, who mentioned the test but had not had it done; from there, I read a little more about it in the popular press. I could not get a doctor to order it for me, but it was a pretty easy process going through Grail's on-line application process with a follow-up phone call. Same $945 self-pay (more expensive now?). They did indicate it was not intended for people on active therapy, so I was happy to use it as a back-up check to Signatera for recurrence or possible presence of other primary tumors before my pancreatic relapse occurred. After informing Grail of its false negative, I had hoped they might contact me for additional details or to offer a refund, LOL. I was disappointed but not surprised to hear nothing from them.

With my dad's mesothelioma, we were also concerned about some possible other primary tumors (prostate and urinary tract, suggested for follow-up after suspicious ultrasound) that might complicate or contraindicate his mesothelioma treatment, but his oncologist was totally dismissive of Grail/Galleri, because it was not yet FDA approved for general diagnostic use (considered OK as a "Lab-Developed Test)" and the PET scan didn't light up those areas as much as the mesothelioma did around his lungs. Too much single focus IMHO, but that's another topic...

Regarding Signatera: My oncology PA said it was not supersensitive for pancreatic cancer either... If negative, you might have cancer, and if positive, you almost definitely have cancer. As Lisa ( @lls8000 ) mentioned, my tumor's mutations were also confirmed by a DNA-based blood test (Guardant) which identified an ATM mutation but noted it could not distinguish somatic (environmental) cause from germline (hereditary) cause.

For Grail, there were early suggestions that it might be sensitive and useful for pancreatic cancer, but that seems to be diminishing over time, or at least the claims are being toned down.

Grail reported the following in 2019 here: https://grail.com/press-releases/grail-announces-positive-new-data-with-multi-cancer-early-detection-blood-test-from-ccga-study/
"Data showed GRAIL’s investigational multi-cancer blood test detected a strong signal for 12 deadly cancer types at early stages with a very high specificity of at least 99 percent (or a false positive rate of one percent or less). In addition, the test identified where the cancer originated in the body (the tissue of origin) with high accuracy...."
and
"...Detection rates (sensitivity) for the 12 deadly cancer types ranged from 59 to 86 percent at early stages (stages I-III). A combined analysis of this group of cancers showed robust detection at early stages (34 percent, 77 percent, and 84 percent at stages I, II, and III, respectively)."

They reported 78% sensitivity for detecting pancreatic cancer between stages 1-3 overall. See the link above for more tables and data.

FWIW, Grail published their 2022 PATHFINDER study summary here:
https://grail.com/press-releases/grail-announces-final-results-from-the-pathfinder-multi-cancer-early-detection-screening-study-at-esmo-congress-2022/
But a 5/11/2023 paper: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10210587/
"Alternatively, most current liquid biopsy tests rely on sequencing and detection of cancer-derived fractions of cell-free DNA (cfDNA) (8). Since many of these tests have been developed for screening average-risk patients, they face challenges for use with high-risk patients. As an example, the commercially-available test, Galleri® by Grail, has a 16.8% sensitivity for stage I pan-cancer, which severely limits the test’s ability to rule out the presence of cancer (9)." -- Reference (9) was published in 2021.

Overall, I'm not against the DNA-based tests; I see them as one tool in the toolbox. If you're asymptomatic and not high-risk, the chance of a false-negative seems low, but don't let that lull you into total complacency. It's always good to verify anything with a second, independent, and hopefully non-invasive method. (e.g., for pancreatic cancer, I also monitored my CA19-9 level, and it was actually an earlier indicator of my recurrence than imaging or Signatera/Grail). If you're higher-risk, symptomatic, or testing positive on any one method, then please waste no time getting an independent follow-up. Time matters, and anything that helps narrow down the diagnosis saves time. Multiple blood tests are easy to do in parallel while you wait for more expensive/invasive scans and biopsies. (For blood tests, ask for germline mutation testing like Invitae and somatic mutation testing like Guardant sooner rather than later.)