Systemd version 256 has been rolled out in several distributions recently, including Arch and Debian and variants. It adds a feature where user sessions are frozen when the system enters sleep, but in my case, running Manjaro Linux with KDE on a Gen 1 Lenovo T14, this meant that when the system woke, the screen remained frozen and required a reboot by switching to the command line with Ctrl-Alt-F3.
At first I perhaps unfairly assumed that this was KDE as it affected the desktop but left the mouse working and indeed the system accessible with through the console, but after a bit of digging around in the system journal with journalctl -b-1 -p4 --no-pager (a really useful command that I didn’t know before), I found the error Cannot start frozen unit Session 10 of User xxxxx from systemd.
Searching on that brought up the problem and conclusively pointed at the 256 update, and a solution, or at least a fix until the issue is fixed.
The fix is to add an override to the systemd-suspend service. This doesn’t actually have a service file in /etc/systemd/system in Manjaro at least, so you need to create the directory /etc/systemd/system/systemd-suspend.service.d and create an override file called disable_freeze_user_session.conf with these contents:

[Service]
Environment="SYSTEMD_SLEEP_FREEZE_USER_SESSIONS=false"

Save this, and restart systemd with systemctl daemon-reload.
This disables user freeze on sleep and for me at least, reverted to the previous behaviour. I found that a lot of the examples mentioned Nvidia video hardware, which I don’t have, so it’s probably a wider issue than I’ve found.
I’ve added a comment to the Github issue.