What upgrades are realistic for a Dell Inspiron 3471?

You can potentially replace the RAM with a 2x16 GB kit and add or replace the storage, but those upgrades will not transform gaming performance. If the computer already has an SSD and you are not running out of memory, putting the money toward a replacement machine will likely provide better value than trying to upgrade the existing chassis.

The biggest limitation is the Dell's small-form-factor design and its roughly 200-watt power supply. That makes normal gaming graphics cards impractical. A low-power, half-height card such as an RX 6400 is about the upper end of what may work, and even then you need to check the exact card dimensions, power requirements, and available slot space. The UHD 630 is integrated graphics, not a separate graphics card. For general work the PC is still perfectly usable, but modern gaming upgrades are very limited.

For substantially better gaming, a newer system or a new build is the more realistic route. The i5-9400 is still adequate for everyday use, but the integrated graphics and restricted power supply prevent a meaningful gaming upgrade. A standard-size computer with a stronger power supply could accept cards such as an RX 6600 or RTX 2070 Super, but those are not suitable assumptions for this Dell SFF system.

Before replacing anything, check whether the storage is an SSD. If it still has a mechanical hard drive, moving Windows and your programs to a SATA SSD will make the system feel dramatically faster, especially during startup and multitasking. Sixteen gigabytes of RAM is generally enough for normal work; upgrading to 32 GB may help only if your workload regularly uses nearly all of the existing memory.