Time to check the main sewer line coming out of your house. Pull the main drain clean out cap and take a look. The drain line should be empty. If it's full you're backed up from a plug or your sewer system is overwhelmed. Can snake for a plug, but be warned that there may not be anywhere for the water to go. My water authority was advising people that the sewer was running slow in places because lift stations were without power.
If your sewer line has standing water, I would not screw the clean out cap back on. Just set it loose on top of the fitting it came out of. If the sewer backup gets worse, hopefully the overflow occurs in your yard instead of your house. Lesser of two evils...