I've read a lot of posts, and with travel coming up next month I'm wondering whether to open another card
Currently I hold the CSP, UAR, Ritz, IHG and Hyatt (these last two are basically sock-drawer cards, just grabbing a free night every year), Citi AA and Barclay HA (opened last year, planning to close), plus two no-annual-fee Freedom cards, BoA 123 (my first card so I've kept it all along), and one Amex to preserve the points from when I closed my Platinum
UAR and Ritz seem to give retention offers every year these past two years, so this year I was originally thinking of closing the UAR but decided to keep it another year, also for the full 8 restaurant PPS visits. After closing it I was planning to open the UAC, and since I'd use the restaurant PPS I want to keep it
My travel frequency these past two years hasn't been as high as before (no more business trips), so I closed both the CSR and Amex Platinum. I always forget about coupon books, especially those monthly credits which are such a pain to use
But I still go abroad for fun every year, once, twice, three times? Depends, no fixed destination, and I don't have a preference for any one hotel chain. Even though high status for upgrades and lounge access was really nice before, without business trips it's hard to maintain on my own, so I've let it go.
Besides rent, my main spending is groceries and dining out, so my Engel coefficient is very high. These past few years, aside from sign-up bonuses, I've basically just used UAR Apple Pay mindlessly
What other cards can I open?
I want something low-maintenance, but if a negative annual fee is really worth it I can make an effort too

You mentioned that the Amex is to keep the points from when you closed the Platinum earlier—so does that mean the one you're keeping now is a no-annual-fee Amex, or something else? This matters for whether you can get the sign-up bonus again later. Also, both the UAR and the Ritz give retention offers—do you call in to ask for them every year, or are they given automatically?