Use the time machine backup drive for tm only.
If you need to transfer files around, get a USB flash drive of sufficient capacity. If you're moving files between the Mac and a PC, format it to exFAT. If it's Mac-only, use HFS+.
If you need an external drive on which to store files "off-Mac", get either a USB hard drive or USB SSD.
I'd suggest something like this:
Samsung T7 Shield Portable SSD delivers high performance on-the-go, not matter the terrain. It has an IP65 rating for water1 and dust2 resistance, with Dynamic Thermal Guard to manage heat control. Transfer huge files instantly. USB 3.2 Gen 2 and PCIe® NVMe achieve soaring sequential read/write ...
www.amazon.com
(that's a great price on it right now)
If it's a platter-based hard drive, format it to HFS+ ("Mac OS extended, journaling enabled, GUID partition format").
If it's an SSD, you can use APFS if you wish -- but for a non-booting drive that is used for data only (and not a tm backup), I'd still suggest HFS+ as "the better way to go".