Folding screen phones like the Samsung Galaxy Z Flip, Motorola Razr, etc. are not “flip phones” in the traditional sense. They are smartphones with a folding screen. If you actually want “simplicity and nostalgia”, then that is a traditional flip phone (which are not smartphones), which is a separate category of device from folding screen phones.
Folding screen phones take all the complexity of any smartphone and add the complexity and fragility of a folding screen mechanism. They are far more fragile than “regular” slab smartphones at this point in their development.
Flip Phones:
The Nokia 2760 is sorta one of these (still comes with a few things like Facebook/Whatsapp/Youtube installed). Samsung is not currently making one. There are a number of other super cheap flip phones running a stripped down version of Android. These are painful to use, as they don’t default to T9 typing, and navigating Android with a keypad and no touchscreen is kinda torture. You can get some decent 3g flip phones still, but very few 4g/5g options exist, and 3g flip phones (or 4G phones that don’t do VOLTE) are now useless on American carriers. The NUU 4L Flip Phone works on 4g and does VOLTE, but the crippled Android interface and default terrible auto capitalization typing mode make it somewhat painful to use.
Some actual still-working-on-VOLTE flip phones:
Nuu 4L Flip
Kyocera’s DuraXV Extreme
Nokia 2760
Cat S22 Flip (Likely only on T-Mobile. Some claim an APN change can make an unlocked one work on Verizon, but many others have failed to get anything other than text messages to work.)