The elderly can be very hard work indeed. I remember when I was a child thinking it was very unfair that my parents used to lie to my grandmother about what we were or weren't doing. I remember being told things like "don't tell grandma we're going on holiday", or "don't tell grandma we've bought a new car". I was too young to understand what was going on behind the scenes when I wasn't there.
As adults, with both me and OH having to care for our respective mothers in old age, I now understand!
We're both honest people (to a fault) and we never lie, not to each other (we don't even do "secret/surprise" things for birthdays etc., not to our son, and not to friends/family or work colleagues, etc.
But, reluctantly, we had to start lying to our respective mothers when they both started getting irrational, illogical and needy.
MIL was the latest and the hardest. She'd always been a pleasant and passive person, always doing things for others, not a hint of selfishness in the near 40 years I knew her. As she lived just 10 minutes away, on a daily basis of us would have been to see her, take her shopping or a drive out, do a bit of gardening for her, do some DIY for her, or some life admin for her. We'd been taking her on family holidays with us and our son for around a decade, but had to stop because of Covid in 2020. So we were (and had been) very engaged with her welfare and included her.
But turning 80, she turned into a monster. Constantly phoning us (several times a day). Getting argumentative about trivial things. Claiming she never saw anyone or did anything (literally once said that on the phone less than an hour after we'd spent half a day with her). Looking back it was clearly the start of dementia or alzheimbers. The first holiday we had without her was when we'd told her we were going somewhere (same kind of place we'd always gone with her, usually European/med resort), and she just point blank refused to come with us, saying she hated going abroad, hated foreigners, etc. So we booked it for us only, and then we had a couple of months of hell with her flip flopping between being angry we weren't taking her and wanting to go. Completely irrational and we'd never seen her like it before. Then that kind of behaviour started in other ways, i.e. refusing to go to Tesco with us, saying she hated it and wanted to go to Sainsbury, then the next week, refusing to go to Sainsbury - exactly the same flip-flopping. It just became easier to not do things with her.
By the time we went on the first holiday without her, she made it a living nightmare for us. Phoning us on our mobiles several times a day, asking when we were coming back, claiming she "needed" us for something that turned out trivial. Next time we went on holiday, we simply didn't tell her and made out we were just at home struck down with a cold and were housebound until we recovered - it was just easier to lie to get her off our backs. (Obviously, we'd made sure she had stocks of food etc in the kitchen but she was still doing small shops herself).
That kind of lying had to become the norm unfortunately as she was ruining our lives with her sudden mood swings, irrationality and neediness. We did have to reduce contact as it was affecting our health. Ironically, the less we did for her and the less we told her, she was actually better and easier to deal with. We could just breeze in, do a bit of irrelevant small talk, check things over, make sure she was OK, and go again, and she'd be fine. But if we told her anything important/relevant, like when our son got a place at Uni, it was back to anger and irrationality, complaining and arguing about why did he need to go to Uni, why spend so much money, if he has to go, why does it have to be so far away, etc. Basically, anything other than her routine and she'd not be able to cope and fly off the handle for no reason. Unfortunately, that meant that instead of us including her in everything, we had to stop telling her things, had to stop doing things with her, etc. Very sad indeed. We knew it wasn't her fault but that doesn't help cope with it.