There is a RealVNC Lite alternative if you look carefully on their website, and that option may well still work for you after June. Unfortunately, RealVNC is pretty good and has excellent mobile clients, so it has long been a first option for many for remote GUI desktop management.
The linked article has some popular alternatives that are cross-platform if RealVNC is no longer going to do the job for you. They do all have some trade-offs, but are free to use.
I’ve already had TightVNC set up as a backup for some of the volunteer work I do, and it does work well from my Linux desktop to the remote Windows desktop (the server side). TigerVNC is another good option to use.
RustDesk is another excellent alternative that is fully cross-platform and probably easiest to set up.
See https://www.techradar.com/best/best-linux-remote-desktop-clients