This question about MTBF is interesting, I learned a little about this parameter years ago, while researching SSD storage.
In the case of this sensor, perhaps the weakest link is the IR emitter.
I found a LASER sensor (680nm) that has a service time of 100,000 hours. It would be interesting if the VL53L5 datasheet had this information, I couldn't find it either.
About MTBF it might be interesting to see these posts:
There has been confusion in understanding the difference between mean time between failures (MTBF) and lifetime. A product might have an MTBF of 500,000 hours, but a lifetime expectancy of 20,000 hours.
https://www.controleng.com/articles/learn-or-review-the-difference-between-mtbf-and-lifetime/
While MTBF can be a useful metric to estimate reliability, especially when comparing components from multiple vendors, the trap many people fall into is wrongly assuming that the MTBF figure directly equates to the expected life of the component. Since there are many misconceptions surrounding this topic in electronic design, it is important to revisit the link between the reliability and lifetime of electronic components.
https://www.cui.com/blog/mtbf-reliability-and-life-expectancy
