The -zapwallettxes functionality has been removed in v0.21.0 (see commit 3340dbadd38f5624642cf0e14dddbe6f83a3863b / PR #19671), with the parameter being kept as hidden option, to inform users via an exit error that abandontransaction should be used instead.
As any guides that still suggest to use -zapwallettxes would refer to a Bitcoin Core version that is EOL since many years (i.e. <= v0.20.x), it is highly unlikely that the error caused by the option is still relevant for any user, hence it seems fine to remove it now.