See release notes at https://github.com/JoinMarket-Org/joinmarket-clientserver/blob/master/docs/release-notes/release-notes-0.5.3.md
Please verify the PGP signatures of the releases before using. They are signed with AdamISZ's pubkey (fingerprint: 2B6F C204 D9BF 332D 062B 461A 1410 01A1 AF77 F20B.
There are several fairly minor bugfixes, but two things of particular note: (1) an improvement to automatic switching of conversations between bots on channels that drop, which became much more relevant since Agora is actively dropping connections during tx negotation (and has been removed from the default config as a result); (2) Several fixes to suboptimal behaviour in the first release (0.5.2) of PayJoin.
In addition to bugfixes, also worthy of note is step-by-step instructions on how to use Joinmarket(+Qt) on Windows 10.