I managed to access OTG drive from within termux without root. #5125

There's a "all files access" (or similar name) in "special app access" (or "special access") setting, find termux and enable it. Some devices require a restart for it to take effect.

Samsung A55:

I forgot to capture id command. On this device, there's special group id 1077 (external_storage) is added to termux. Everything else is the same.

~ $ id
uid=10348(u0_a348) gid=10348(u0_a348) groups=10348(u0_a348),1077(external_storage),3003(inet),9997(everybody),20348(u0_a348_cache),50348(all_a348) context=u:r:untrusted_app_27:s0:c92,c257,c512,c768