The default OT1 encoding has various curious properties as it supports only 128 chars and should better be avoided. Load always T1 with pdflatex.
– Ulrike FischerApr 17 '22 at 12:39
Check the font table in texdoc encguide -- actually not there's only table of cmr10 here not cmtt10 -- nevertheless cmtt10 font does have {}, but not cmr10.
– user202729Apr 17 '22 at 12:45
Wait actually it's duplicate of https://tex.stackexchange.com/questions/181118/how-to-escape-curly-braces-within-texttt?rq=1 (just notice it on the related question) but the answer there is a little worse...
– user202729Apr 18 '22 at 05:43
@user202729 Well, I searched the key words before asking the question but didn't find it....
– M. LogicApr 18 '22 at 05:45
I didn't find it either, only notice it only related panel to the right -- anyway having more question for signpost might be useful.
– user202729Apr 18 '22 at 05:45
\usepackage[T1]{fontenc}. – Ulrike Fischer Apr 17 '22 at 12:27texdoc encguide-- actually not there's only table of cmr10 here not cmtt10 -- nevertheless cmtt10 font does have {}, but not cmr10. – user202729 Apr 17 '22 at 12:45