It depends on the country one lives in, because to connect equipment to the grid, it has to be certified in that country.

As a good starting point, I would recommend to look at inverters sold as “hybrid inverters”, especially if the manufacturer advertises “off-grid” capability. Typically there’s a process of automatic switch-over and it has to take really few milliseconds (e.g. 10 ms).

Here is one, from the manufacturer whose devices (older version) I use. There are many others. If the user’s manual explains the process of automatic switch-over to off-grid (island) mode, then the inverter will provide autonomous power in case of grid collapse.

maximumsolar.online/product/hybridv2-6048/

…and here is another one, from a different company. Anything that becomes autonomous upon loss of grid freqency (disconnects from the grid and leaves only sensors to read its status) and then gracefully handles the return of grid frequency (does not connect before synchronization has been achieved).

qoltec.com/…/qoltec-hybrid-solar-inverter-off-gri…