It's a long story, but I'll keep it brief. The last planned outing for my Dinner Jacket (Tuxedo, y'all) was to have been the Orient Express in 2019, it was then to be consigned to a charity shop in Venice as my days of dressing to conform to the pretentions or insecurities of others are behind me. The reliable staff of SNCF helpfully declared a strike on the very day that the OE would have passed through Paris and the venture was cancelled. I'll confess to being relieved.
You're right, I'm unfamiliar with luxury train travel - being resident in the UK, that's normal.
If you were to use the west-coast 'main line' service from the North West of England to London, the passengers have been known to break into spontaneous applause if the train actually arrives at the destination, regardless of the arrival time. I was once stranded on the service for eight hours by flooding both in front and behind. The water supply failed and the only available liquid was an inordinate supply of Red Stripe strong beer. My carriage was comprised of myself and a 50/50 mix of Glaswegian football supporters and what must have been an entire convents-worth of nuns. After several hours and with the only refreshment available being consumed liberally (the weegies thought they were in heaven, the nuns in hell), the train was finally able to move off - but only back to the start point; so we never got to London.
I have used the RENFE Trenhotel in the past and that surpassed my expectations, which is my definition of a good experience.