Date: 202006
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Aircraft: Small Aircraft
Flight plan: IFR
Flight phase: Final Approach
Airspace: Class E ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Distraction; Situational Awareness; Workload
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Detector: Person Air Traffic Control
Contributing factors: Environment - Non Weather Related; Procedure; Human Factors
Primary problem: Human Factors

Narrative: I was working 2 sectors at the time of the event; XX and XY. We had previously moved around positions around the room several times before this actual configuration; but this configuration is how things were normally done before the COVID scheduling. The event is as follows: Aircraft X is going to ZZZ from the west and requests the RNAV RWY X Approach into ZZZ airport. I glance at the NOTAMs and the procedure; and clear them to cross ZZZZZ (the IF) at or above 150 to meet terrain (XXX) and the crossing restriction of ZZZZZ (XXY). The pilot continues to descend the aircraft for the approach at ZZZZZ to XXY; but is now below the terrain on an unauthorized approach. The aircraft was cleared for the approach at [time] and canceled IFR moments later after going below the MEA or MIA at ZZZ Center.I feel there were several factors leading to the event. Most notably would be the way ERIDS [En Route Information Display System] shows us our NOTAMs. Typically you read over the NOTAMs in a quick fashion when your busy and discard the long NOTAMs that never say anything important. Any NOTAMs that come after these elongated NOTAMs are typically not applicable as well. In this particular instance; the very last NOTAM listed was very much applicable saying this approach to ZZZ airport (the RNAV to RWY X) is NA (not authorized) even though it's been published for several months.The next factor is the complexity. Before these last 2 days of work; I had previously never worked a busy session since COVID scheduling began. I wanted to switch back to days to continue to hone my skills as a Controller and I believe I have; but that still doesn't take into account how busy things have picked back up and how available people are during a day shift for help if it's needed (which there is not).The next factor was traffic volume. I was fairly busy dealing with multiple things all over the sectors and that probably didn't help when it came time to look at the NOTAMs for this specific airport. I probably glanced over something that should have in my opinion jumped out at me more.The next is the way we are briefed for these things. Being briefed for this new approach probably happened prior to the COVID scheduling and with so much time in between now and then; it is just a lost thought. I never even knew we had an approach to RWY X at ZZZ airport in State X until this aircraft requested it. And that goes into my next point.Typically pilots don't request something that is NOTAMed Not Authorized or closed; but I didn't just have 1 aircraft request that approach today; I had several. All about 15 mins-20 mins apart. This is the only instance in which I cleared them and they got below terrain before canceling IFR; but it was still an issue.I would recommend a different way to show NOTAMs on our ERIDS at the facility. Too often we miss something as we read over them because the very elongated NOTAMs are never applicable and NOTAMs that come after them are almost never read.The second thing I recommend is to be briefed better on items such as this. Maybe I was briefed on the approach earlier in the year; but to know that now the procedure is NOTAMed NA is a different thing entirely. Sheets should be posted on the position that controls those aircraft and briefed prior to taking the position every time; which it was not.I also feel I could do a much better job at reading the NOTAMs entirely.




Synopsis: Center Controller reported clearing an aircraft for a NA (Not Authorized) Approach; and observing the aircraft descend below the MEA.