I am a manager (indirect to this person) in a small UK based company and work with a fantastic colleague/friend who is rapidly approaching complete burnout. The job is non-physical, involves data/statistics and is conducted primarily whilst working from home. They seem unable to switch off from work, always trying to be available, assisting other employee's tasks during their own non-working hours, frequently working very unsocial and unsustainable hours (e.g: sometimes 20 hours at a time). They do considerably more than what is expected of them. I appreciate that they are an adult and their decisions are their own, but I am very concerned about their health.
They book holiday but don't really take the time off, instead they are checking emails, company messaging apps and accessing parts of the system in order to provide stats and answers to other employees, or just continuing their own work.
Direct management and myself have tried on many occasions to discuss with them about their working behaviour, that it isn't necessary and we don't want them putting so much of a strain on themselves, but the message doesn't seem to be getting through.
How can we further assist this employee to actually disconnect from work? We've tried stocking them up with additional PTO to compensate for the additional hours of work being provided, but believe the employee just typically works through those as well.
We are at the stage where we're considering suspending email/system/contact apps for the duration of their booked holiday time to forcefully prevent them from accessing work, but we wouldn't want that run foul of any potential employment laws. It may seem a be dramatic/over the top, but would that be in our rights? Any other answers, or recommendations to not do that are also welcome.
edit, additional background info:
Conversations with my colleague about why they are working so many hours focus around priority and a self-determined urgency. They are a manager themselves (but this sense of urgency/"now now now" is thankfully not distributed to their team) but are always way too critical of their own work, for example they express that "they could have done better" or "could have done this sooner". This does not mirror the feedback they receive on their work, which is typically very positive.
I believe they want to over-perform in all areas, even those in which they should only be involved to a minor extent. Trying to establish why they are contributing such huge efforts has been difficult, as they have admitted they don't really know where they want to go in terms of progression, or if they even necessarily want to "progress". I personally do not believe any level of promotion would adjust the way they work, they constantly want to produce all work to the highest standard possible, which isn't feasible.
They have a very strong work ethic, which whilst typically a good thing, is contributing to their problems. In recent conversations they are self-aware of this and even agree, they just find it incredibly hard or seemingly impossible to stop.