Created attachment 180680 [details] after typing quote 1) type a single or double quote 2) Undo - observe the quote char does not go away, but it changes to a simplified quote char 3) Undo - observe this time the char goes away
Created attachment 180681 [details] after one Undo
Created attachment 180682 [details] sample file but nothing special, will occur in a new file
Confirm with Version: 7.4.0.0.alpha1+ / LibreOffice Community Build ID: d4123356c61db269651e950a0a2cc93e6d801c90 CPU threads: 4; OS: Linux 5.13; UI render: default; VCL: x11 Locale: cs-CZ (cs_CZ.UTF-8); UI: en-US Calc: threaded Jumbo not in Version 4.1.0.0.alpha0+ (Build ID: efca6f15609322f62a35619619a6d5fe5c9bd5a), but here is simplified quote written. Please try turn off Tools - Autocorrect - tab Localized Options - Single quotes replace. So, second undo is for autocorrect replacement. For me not a bug.
If I turn off autocorrect 'while typing' then the I get an unstyled quote and one Undo actually undoes it.
This is explained as NotABug.